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Once again, about "time decay"

Once again, about "time decay"# Stock

j*b2011-10-12 07:10

1 楼

Time decay is kind of mystified here. It is not magic.
For example, people talk about shorting tna and tza at the same time. Lets
take a look at such a trade.
Imagine you short $10,000 worth of TNA and TZA both. So you need a fund of $
20,000. Imagine IWM first go down 3% and then up 3%. So TNA and TZA go up 9%
and down 9% in different order, and both becomes 99.19% of the original
value, and you pocket a profit of .81%, or $162.
Now imagine instead of doing the above trade, you buy $5400 worth of iwm
when it went down by 3%, then sell it when it went up 3%, you will pocket a
profit of about $162, with a fund of just $5400.
These two trades have the same profit because they basically did the
same. But then they are different.
The difference is not just $20,000 vs $5400. In the first trade, your
positions are much more dangerous. You may get margin call very quickly if
the market goes in one direction too much.

B*r2011-10-12 07:10

2 楼

You made a wrong, and unfair assumption to your favor.
When you evaluate other people's TNA/TZA short, you assume the market is
neutral. But when you evaluate your IWM trade, you assume you made the right
call. What if the market moves against your will?

$
9%
a

【在 j***b 的大作中提到】

: Time decay is kind of mystified here. It is not magic.
: For example, people talk about shorting tna and tza at the same time. Lets
: take a look at such a trade.
: Imagine you short $10,000 worth of TNA and TZA both. So you need a fund of $
: 20,000. Imagine IWM first go down 3% and then up 3%. So TNA and TZA go up 9%
: and down 9% in different order, and both becomes 99.19% of the original
: value, and you pocket a profit of .81%, or $162.
: Now imagine instead of doing the above trade, you buy $5400 worth of iwm
: when it went down by 3%, then sell it when it went up 3%, you will pocket a
: profit of about $162, with a fund of just $5400.

j*b2011-10-12 07:10

3 楼

No it's not unfair.
Time decay is realized by adjusting position (done automatically through the
use of leveraged etf), the second trade did the same thing -- adjusting
position, just manually.

right

【在 B**********r 的大作中提到】

: You made a wrong, and unfair assumption to your favor.
: When you evaluate other people's TNA/TZA short, you assume the market is
: neutral. But when you evaluate your IWM trade, you assume you made the right
: call. What if the market moves against your will?
:
: $
: 9%
: a

u*e2011-10-12 07:10

4 楼

I guess the comparison should be $162 for shorting both versus $0 for buying
IWM if the IWM went down 3% first and went back up 3.09%.
The $162 profits could be a rewarded for the possible margin call losses

$
9%
a

【在 j***b 的大作中提到】

B*r2011-10-12 07:10

5 楼

Please check the 1-year chart of IWM, TNA, and TZA, 10/12/2010-10/12/2011
If you long IWM with full account value, you get 0% return in 1 year.
I short TNA/TZA, say 1/3 on TNA and 1/3 on TZA. TNA is down 20% and TZA is
down 46%. My return is +25%.
And, 1/3 TNA short and 1/3 TZA short, together, has lower leverage than 100%
in IWM.

$
9%
a

【在 j***b 的大作中提到】

j*b2011-10-12 07:10

6 楼

You are right, I miscalculated a little. But the difference is very slight.
My point is that you can get the same profit of $162 the same way without
risking margin calls

buying

【在 u********e 的大作中提到】

: I guess the comparison should be $162 for shorting both versus $0 for buying
: IWM if the IWM went down 3% first and went back up 3.09%.
: The $162 profits could be a rewarded for the possible margin call losses
:
: $
: 9%
: a

h*n2011-10-12 07:10

7 楼

In the first case, you short without a condition.
In the second case, you buy with a condition.
You can not compare these two because the second trade would not exist if
the condition does not meet.
How about just compare buy now and the market down 3% and then up 3%. You
made profit on the first trade while no profit on the second.

$
9%
a

【在 j***b 的大作中提到】

j*b2011-10-12 07:10

8 楼

The problem is can you short both position with you entire account? No right
? Do you know why? Because these trades have high beta.
Shorting 3x etf for time decay is basically the good old gambling trick of "doubling my bet if I lose". You are guaranteed to win if you have infinite capital.

100%

【在 B**********r 的大作中提到】

: Please check the 1-year chart of IWM, TNA, and TZA, 10/12/2010-10/12/2011
: If you long IWM with full account value, you get 0% return in 1 year.
: I short TNA/TZA, say 1/3 on TNA and 1/3 on TZA. TNA is down 20% and TZA is
: down 46%. My return is +25%.
: And, 1/3 TNA short and 1/3 TZA short, together, has lower leverage than 100%
: in IWM.
:
: $
: 9%
: a

L*J2011-10-12 07:10

9 楼

time decay不能算myth吧，看看8/8和10/3的TZA就是了，在IWM新低的情况下，TZA却还
离高点有10%。
不过能不能吃到那是另外一回事，我看不见得比DT fasfaztnatza来得容易，或者说谈
不上风险free

l*n2011-10-12 07:10

10 楼

强力支持技术贴！

j*b2011-10-12 07:10

11 楼

It's not myth, but people mystified it here. That's my point.

【在 L**J 的大作中提到】

: time decay不能算myth吧，看看8/8和10/3的TZA就是了，在IWM新低的情况下，TZA却还
: 离高点有10%。
: 不过能不能吃到那是另外一回事，我看不见得比DT fasfaztnatza来得容易，或者说谈
: 不上风险free

B*r2011-10-12 07:10

12 楼

You have difficulties understanding English. I said 1/3 of account short TNA
, and 1/3 short TZA. The return is 25% in 1 year, and it is much safer than
100% in IWM with 0% return.
If you still do not admit you are wrong, I have no other words.

right
"doubling my bet if I lose".

【在 j***b 的大作中提到】

: The problem is can you short both position with you entire account? No right
: ? Do you know why? Because these trades have high beta.
: Shorting 3x etf for time decay is basically the good old gambling trick of "doubling my bet if I lose". You are guaranteed to win if you have infinite capital.
:
: 100%

r*l2011-10-12 07:10

13 楼

其实简单点说吧，同时short能赚钱，留3倍的空间，否则很容易margin call

j*b2011-10-12 07:10

14 楼

You still didn't get it, in both trade, the key is ADJUSTING POSITION. It's
just the difference of doing it automatically or manually.

【在 h****n 的大作中提到】

: In the first case, you short without a condition.
: In the second case, you buy with a condition.
: You can not compare these two because the second trade would not exist if
: the condition does not meet.
: How about just compare buy now and the market down 3% and then up 3%. You
: made profit on the first trade while no profit on the second.
:
: $
: 9%
: a

j*b2011-10-12 07:10

15 楼

The last time I remember you said your position were very small.
I think if you really used 2/3 of your account, you will get margin call.

TNA
than

【在 B**********r 的大作中提到】

: You have difficulties understanding English. I said 1/3 of account short TNA
: , and 1/3 short TZA. The return is 25% in 1 year, and it is much safer than
: 100% in IWM with 0% return.
: If you still do not admit you are wrong, I have no other words.
:
: right
: "doubling my bet if I lose".

j*b2011-10-12 07:10

16 楼

After further checking, I was right in my original post.

buying

【在 u********e 的大作中提到】

h*n2011-10-12 07:10

17 楼

If the key is adjusting position, that is no point to discuss.
The trades relies on tomorrow, every tomorrow. All discuss on a trade
strategy is useless if it depends on every next moment.
The focus should be which trade strategy that can survive every market changes.

s

【在 j***b 的大作中提到】

: You still didn't get it, in both trade, the key is ADJUSTING POSITION. It's
: just the difference of doing it automatically or manually.

j*b2011-10-12 07:10

18 楼

My second trade is not based on tomorrow, it the good old strategy of buying
dip.

【在 h****n 的大作中提到】

: If the key is adjusting position, that is no point to discuss.
: The trades relies on tomorrow, every tomorrow. All discuss on a trade
: strategy is useless if it depends on every next moment.
: The focus should be which trade strategy that can survive every market changes.
:
: s

h*n2011-10-12 07:10

19 楼

if the price drop 2% and then go up 4%, where is your trade?

buying

【在 j***b 的大作中提到】

: My second trade is not based on tomorrow, it the good old strategy of buying
: dip.

o*y2011-10-12 07:10

20 楼

what is your IQ in righting this post...
no logic at all
not equal comparison at all

j*b2011-10-12 07:10

21 楼

The key is delta, you can adjust your account to any delta.
In my two examples, for the first trade, the delta for three days are
0
$5,400
0
For the second trade, the delta is
0
$5,400
0
You can always adjust your account to any delta at close, so these are very
fair comparison.

【在 h****n 的大作中提到】

: if the price drop 2% and then go up 4%, where is your trade?
:
: buying

h*n2011-10-12 07:10

22 楼

逻辑呀逻辑
我说如果keep adjust就没有讨论的必要了。因为adjust base on future,future不停
的变，就不停的adjust。那么讨论一个strategy就没有意义了.需要讨论的是一个
strategy在不停变化的市场条件下的实用性。
然后你和我说你的trade不是based on tomorrow.我随便举了个市场变化的例子，你有
说adjust position.
你到底adjust不adjust base on future market呢？
发信人: jszhb (金嗓子喉宝), 信区: Stock
标题: Re: Once again, about "time decay"
发信站: BBS 未名空间站 (Wed Oct 12 12:42:35 2011, 美东)
My second trade is not based on tomorrow, it the good old strategy of buying
dip.

very

【在 h****n 的大作中提到】

j*b2011-10-12 07:10

23 楼

Buying dip is not based on future.
The second trade buys the 3% dip, isn't that quiet clear, where is it "based
on future"?

【在 h****n 的大作中提到】

: 逻辑呀逻辑
: 我说如果keep adjust就没有讨论的必要了。因为adjust base on future,future不停
: 的变，就不停的adjust。那么讨论一个strategy就没有意义了.需要讨论的是一个
: strategy在不停变化的市场条件下的实用性。
: 然后你和我说你的trade不是based on tomorrow.我随便举了个市场变化的例子，你有
: 说adjust position.
: 你到底adjust不adjust base on future market呢？
: 发信人: jszhb (金嗓子喉宝), 信区: Stock
: 标题: Re: Once again, about "time decay"
: 发信站: BBS 未名空间站 (Wed Oct 12 12:42:35 2011, 美东)

h*n2011-10-12 07:10

24 楼

Then answer my question?
发信人: hatwin (傻就一个字), 信区: Stock
标题: Re: Once again, about "time decay"
发信站: BBS 未名空间站 (Wed Oct 12 12:43:26 2011, 美东)
if the price drop 2% and then go up 4%, where is your trade?

buying
based

【在 j***b 的大作中提到】

: My second trade is not based on tomorrow, it the good old strategy of buying
: dip.

h*n2011-10-12 07:10

25 楼

发信人: hatwin (傻就一个字), 信区: Stock
标题: Re: Once again, about "time decay"
发信站: BBS 未名空间站 (Wed Oct 12 12:34:16 2011, 美东)
In the first case, you short without a condition.
In the second case, you buy with a condition.
You can not compare these two because the second trade would not exist if
the condition does not meet.

【在 h****n 的大作中提到】

: Then answer my question?
: 发信人: hatwin (傻就一个字), 信区: Stock
: 标题: Re: Once again, about "time decay"
: 发信站: BBS 未名空间站 (Wed Oct 12 12:43:26 2011, 美东)
: if the price drop 2% and then go up 4%, where is your trade?
:
: buying
: based

j*b2011-10-12 07:10

26 楼

My post about "delta" put it very clear. I can't help you if you can't
understand it.

h*n2011-10-12 07:10

27 楼

对嘛，就说你的讨论是based on adjust "delta" （adjust based on future market）就行了。何必不承认就是adjust的一种操作呢？只要是时时adjust的操作，风险自然被降低。可操作性就要降低，利润率也要降低。

【在 j***b 的大作中提到】

: My post about "delta" put it very clear. I can't help you if you can't
: understand it.

j*b2011-10-12 07:10

28 楼

know what is delta and then talk.

market）就行了。何必不承认就是adjust的一种操作呢？只要是时时adjust的操作，风
险自然被降低。可操作性就要降低，利润率也要降低。

【在 h****n 的大作中提到】

: 对嘛，就说你的讨论是based on adjust "delta" （adjust based on future market）就行了。何必不承认就是adjust的一种操作呢？只要是时时adjust的操作，风险自然被降低。可操作性就要降低，利润率也要降低。

h*n2011-10-12 07:10

29 楼

delta随市场时间而变化，如果你的trade因此而调整就是trade based on future
market.我仅仅指出这一点，你让我学习delta,你到底想表达什么呢？难道你想说如果我学习了delta，你的就不是adjust based on future market的操作了？

【在 j***b 的大作中提到】

: know what is delta and then talk.
:
: market）就行了。何必不承认就是adjust的一种操作呢？只要是时时adjust的操作，风
: 险自然被降低。可操作性就要降低，利润率也要降低。

j*b2011-10-12 07:10

30 楼

Who told you "delta随市场时间而变化"?
If you by $1 of stock, you have $1 delta of that stock.
If you buy $1 of TNA, your have $3 delta of iwm.

【在 h****n 的大作中提到】

: delta随市场时间而变化，如果你的trade因此而调整就是trade based on future
: market.我仅仅指出这一点，你让我学习delta,你到底想表达什么呢？难道你想说如果我学习了delta，你的就不是adjust based on future market的操作了？

B*r2011-10-12 07:10

31 楼

There is no need to further argue with him. He is stupid and stubborn.

【在 h****n 的大作中提到】

h*n2011-10-12 07:10

32 楼

tomorrow the stock becomes $0.5,what is the delta?

【在 j***b 的大作中提到】

: Who told you "delta随市场时间而变化"?
: If you by $1 of stock, you have $1 delta of that stock.
: If you buy $1 of TNA, your have $3 delta of iwm.

j*b2011-10-12 07:10

33 楼

$.5

【在 h****n 的大作中提到】

: tomorrow the stock becomes $0.5,what is the delta?

h*n2011-10-12 07:10

34 楼

Who told you "delta随市场时间而变化"?
you just told me.
逻辑呀

【在 j***b 的大作中提到】

: $.5

j*b2011-10-12 07:10

35 楼

stupid people just know personal attack, instead of technical stuff.
Every time I discuss something technical, you have to turn it into personal attack.

【在 B**********r 的大作中提到】

: There is no need to further argue with him. He is stupid and stubborn.

j*b2011-10-12 07:10

36 楼

delta随市场时间而变化，如果你的trade因此而调整就是trade based on future
How is it depend on future?
today's delta depends on today, future's delta depends on future.
If today the stock worth $1, it's delta is $1, so that if it drops 50%, you
lose $1*50%.
When you buy a stock, your current delta is based on the current stock price, not future price.
Now you understand it?

【在 h****n 的大作中提到】

: Who told you "delta随市场时间而变化"?
: you just told me.
: 逻辑呀

b*r2011-10-12 07:10

37 楼

我烧过3X对冲组合，实际操作中确实有收到broker强迫买回的警告。
所以单边市场里这样做不太容易，如果trading size太大，几乎肯定有一腿
要被强迫敲掉。
烧一点点玩的，不在这个讨论范围。
在range market里烧，应该是很好的选择。

$
9%
a

【在 j***b 的大作中提到】

h*n2011-10-12 07:10

38 楼

我觉得你在自己交易的框框里面绕。别人用的语言和词语，你加上自己框框里面的理解
，就绕呀绕。你以为别人不明白你的意思，实际上是你没有心思听别人的意思。还在自
己的框框里面绕。
总的来说你比较2个交易，一个是同时short 两边，一个是单边作long.你想同过
假设市场现降3%再升3%来说明这两个交易的好坏。但是你暗示的条件是不平等的。同时short立刻交易。然后市场变化down 3%，再升 3%。而作long的交易，要等，等到市场先down 3%之后，在入场。我指出这一点，你就开始用delta来绕。这两个交易不同时开始delta怎么一定一样呢？说不定第一个交易早1个星期就开始了。等了一个星期，market才down了3%，可以开始第二个交易了。你就用你的delta来证明不是based on future的交易.否则就是理解错了delta.
好了，我不玩了，你继续吧。

you
price, not future price.

【在 j***b 的大作中提到】

: delta随市场时间而变化，如果你的trade因此而调整就是trade based on future
: How is it depend on future?
: today's delta depends on today, future's delta depends on future.
: If today the stock worth $1, it's delta is $1, so that if it drops 50%, you
: lose $1*50%.
: When you buy a stock, your current delta is based on the current stock price, not future price.
: Now you understand it?

j*b2011-10-12 07:10

39 楼

I whose 词语 delta refers to future delta? So how to you answer when people
ask you "what is your delta"? Do you give him your current delta, or you say
"well, if the market goes to zero tomorrow, then my delta will be 0, on the
other hand, if the market goes up 1000000%, then my delta will be pretty
big. So basically, my delta is between 0 and infinity".
Or it's like people ask you how much money you have in your bank account? You say "if I suddenly made a fortune then I will have a lot of money. But if someone steal my entire account, then I will have no money. So my money in the account is between 0 and infinity ".

时short立刻交易。然后市场变化down 3%，再升 3%。而作long的交易，要等，等到市
场先down 3%之后，在入场。我指出这一点，你就开始用delta来绕。这两个交易不同时
开始delta怎么一定一样呢？说不定第一个交易早1个星期就开始了。等了一个星期，
market才down了3%，可以开始第二个交易了。你就用你的delta来证明不是based on
future的交易.否则就是理解错了delta.

【在 h****n 的大作中提到】

: 我觉得你在自己交易的框框里面绕。别人用的语言和词语，你加上自己框框里面的理解
: ，就绕呀绕。你以为别人不明白你的意思，实际上是你没有心思听别人的意思。还在自
: 己的框框里面绕。
: 总的来说你比较2个交易，一个是同时short 两边，一个是单边作long.你想同过
: 假设市场现降3%再升3%来说明这两个交易的好坏。但是你暗示的条件是不平等的。同时short立刻交易。然后市场变化down 3%，再升 3%。而作long的交易，要等，等到市场先down 3%之后，在入场。我指出这一点，你就开始用delta来绕。这两个交易不同时开始delta怎么一定一样呢？说不定第一个交易早1个星期就开始了。等了一个星期，market才down了3%，可以开始第二个交易了。你就用你的delta来证明不是based on future的交易.否则就是理解错了delta.
: 好了，我不玩了，你继续吧。
:
: you
: price, not future price.

j*b2011-10-12 07:10

40 楼

A little more on "time decay".
In my earlier posts I mentioned that time decay from 3x etfs can be totally
replicated by adjusting position. Of course adjusting position manually,
first, it takes some work, then there is the problem of commission and bid-
ask spread. Clearly 3x etf has the advantage of automatically adjusted (
almost) free of charge and daily.
But you need to realize that you don't need to adjust closely as often as
daily, because most of the "time decay" are generated from the few days when
there are big ups and downs. For example, if the market only moves 0.5%,
then the time decay is about 0.0225%. So if you invest $10,000, profit from
decay is just $1.125 in one day. So you earn next to nothing in decay in
those piggy days. How much you can earn by selling options? Much more.
On the other hand, if the market moves 5%, then the decay is 1.125%, that
means profit of $112.5 from the decay.
So, if you just capture the decay of the few violent days, you won't miss
much.
And on another note, it also tells the truth that the time decay are
mostly earned from the risky trading during the most violent days. That's
not easy money I have to say.

h*n2011-10-12 07:10

41 楼

虽然你比较死脑筋，但是还是很用心的蛮执着。呵呵
看到你这样的人还是蛮有趣儿的。可惜你始终还是在自己的想法里面。如果你借鉴一下
别人的看法，就可能跳出自己固定思维的圈子。毕竟提高自己才是最重要的。
你所举的第一个交易例子实际上是赚time decay的操作。因为价格先降后升，虽然目标
价格相对没变，但赚到了time decay的利润。你所举的第二个交易例子实际上是赚波段
的操作。
如果一切都像计划的一样，你的结论肯定是正确的。time decay的利润怎么可能和做股
票吃波段的利润比呢？如果你加上option单边吃波段，利润肯定比股票单边吃波段的更
大。
但是因为波段不好判断，单边交易万一错了损失是很大的，因此才能谈到吃time decay
的操作的好处。
如果能够预测准确波段
option 波段利润> stock 波段利润> short 双向time decay利润（同样的投入。
如果不同样的投入，同样利润情况下，回报率自然从高到低）。
如果不能准确预测波段,显然风险
option > stock > short 双向
这么明显的交易计划比较，由于你加上一些数学概念(delta)，把简单的问题复杂化了
，还有心理总有不停adjust trades的概念在里面。然后就以为发现了一个关于time
decay的新操作。你的思考方式不是很open,总觉得大家没有理解你,只是专注在你的思
维里面，拼命解释。
其实你说的东西本身就是个事实（股票波段利润高于time decay利润），不用多解释，大家都明白的。
如果你能发现一种adjust方法可以弥补波段预测的不准确性，那就很有意义了。

totally
when
from

【在 j***b 的大作中提到】

: A little more on "time decay".
: In my earlier posts I mentioned that time decay from 3x etfs can be totally
: replicated by adjusting position. Of course adjusting position manually,
: first, it takes some work, then there is the problem of commission and bid-
: ask spread. Clearly 3x etf has the advantage of automatically adjusted (
: almost) free of charge and daily.
: But you need to realize that you don't need to adjust closely as often as
: daily, because most of the "time decay" are generated from the few days when
: there are big ups and downs. For example, if the market only moves 0.5%,
: then the time decay is about 0.0225%. So if you invest $10,000, profit from

j*b2011-10-12 07:10

42 楼

I've been trying to be technical, not personal, but a couple of IDs such as
you and the other one kept being personal.
Just to point this out in case someone says I'm trying to pick a fight.

decay

【在 h****n 的大作中提到】

: 虽然你比较死脑筋，但是还是很用心的蛮执着。呵呵
: 看到你这样的人还是蛮有趣儿的。可惜你始终还是在自己的想法里面。如果你借鉴一下
: 别人的看法，就可能跳出自己固定思维的圈子。毕竟提高自己才是最重要的。
: 你所举的第一个交易例子实际上是赚time decay的操作。因为价格先降后升，虽然目标
: 价格相对没变，但赚到了time decay的利润。你所举的第二个交易例子实际上是赚波段
: 的操作。
: 如果一切都像计划的一样，你的结论肯定是正确的。time decay的利润怎么可能和做股
: 票吃波段的利润比呢？如果你加上option单边吃波段，利润肯定比股票单边吃波段的更
: 大。
: 但是因为波段不好判断，单边交易万一错了损失是很大的，因此才能谈到吃time decay

b*n2011-10-12 07:10

43 楼

这种文章也m?
用apple 比 orange, 基本逻辑都不对.

$
9%
a

【在 j***b 的大作中提到】

j*b2011-10-12 07:10

44 楼

They are exactly the same thing delta wise. How is that comparing apple to
orange?

【在 b******n 的大作中提到】

: 这种文章也m?
: 用apple 比 orange, 基本逻辑都不对.
:
: $
: 9%
: a

h*n2011-10-12 07:10

45 楼

哦，如果我说什么冒犯你了，请消气。没有别的意思。
在这里向你道歉了（我的确不该说你死脑筋，固执，不open什么的，以股票市场的经历来看，我的判断都是不准确的。哈哈）。
呵呵

as

【在 j***b 的大作中提到】

: I've been trying to be technical, not personal, but a couple of IDs such as
: you and the other one kept being personal.
: Just to point this out in case someone says I'm trying to pick a fight.
:
: decay

h*y2011-10-12 07:10

46 楼

the difference is very slight？
打回重写；

【在 j***b 的大作中提到】

: You are right, I miscalculated a little. But the difference is very slight.
: My point is that you can get the same profit of $162 the same way without
: risking margin calls
:
: buying

j*b2011-10-12 07:10

47 楼

As I mentioned, I checked again and I was right, so no need to 重写.

【在 h*******y 的大作中提到】

: the difference is very slight？
: 打回重写；

j*b2011-10-12 07:10

48 楼

It will be pretty close to 20K for IB for usual account.
Margin requirement for 3x etf is very high.
Buying dip is not timing the market. It dips --- buy, no dip --- don't buy, dip further after dipped, buy more. See, no timing.

trying

【在 b******n 的大作中提到】

: 这种文章也m?
: 用apple 比 orange, 基本逻辑都不对.
:
: $
: 9%
: a

j*b2011-10-12 07:10

49 楼

Lol. That some big suggestions. I will suggest you a little differently,
just know what is delta, and read my earlier posts about delta, so that you
can understand what I'm talking about.

【在 b******n 的大作中提到】

: 这种文章也m?
: 用apple 比 orange, 基本逻辑都不对.
:
: $
: 9%
: a

s*e2011-10-12 07:10

50 楼

I think your hunch is essentially correct although your example and
explanation wasn't great.
Unfortunately very few people got it including someone who seem to work on
the street.

$
9%
a

【在 j***b 的大作中提到】