l*n
2 楼
a. d 一样?
w*n
3 楼
B
s*s
4 楼
肿觉没一个对的
t*n
5 楼
b不对吧。
随便选有50%机会选中B?
这题没有答案吧
随便选有50%机会选中B?
这题没有答案吧
s*d
7 楼
题目错误怎么能找到正确答案?
g*a
9 楼
i thought the probability would be 1/3.
b*n
10 楼
Suppose we randomly pick a, b, c, and d, then
if a/d is correct, the chance to be correct is 50%
if b is correct, the chance to be correct is 25%
if c is correct, the chance to be correct is 25%
Let P(a/d) to be the possibility of a/d is the correct answer
P(b) to be the possibility of b is the correct answer
P(c) to be the possibility of c is the correct answer
and P(total) to be the possibility of getting the correct answer
Then we have
P(total) = P(a/d) * 50% + P(b) * 25% + (1-P(a/d)-P(b)) * 25%
= P(a/d)*0.5 + P(b)*0.25 + 0.25 - P(a/d)*0.25 - P(b)*0.25
= P(a/d)*0.25 + 0.25
Since one of the answers is correct, P(total) would have value of 25%,
50%
or 60%.
if P(total) = 0.25, we get P(a/d) = 0, which means a, d is not the
correct
answer, which is a conflict.
if P(total) = 0.5, we get P(a/d) = 1, which means only a, d can be the
correct answer, which is also a conflict (since P(total)=0.5 means b is
the
correct answer)
if P(total) = 0.6, we get P(a/d) = 1.4, which is not possible.
Therefore this question has no answer.
However, if either b or c is in the range of (0.25, 0.5), then we can
possibly get a correct answer based on P(a/b).
For example, if choice b is 45%, c is something else (not 25% or 45%).
Then
for P(total) = 0.45, we get P(a/d) = 0.8. In that case, as long as a/d
has
80% chance to be the correct answer, the possibility that we pick the
correct answer will be exactly 45%. Since
P(total) = P(a/d)*0.5 + P(b)*0.25 + P(c)*.025
= P(a/d)*0.5 + (P(b)+P(c)) * 0.25
= 0.8 * 0.5 + 0.2 * 0.25
= 0.45
#
if a/d is correct, the chance to be correct is 50%
if b is correct, the chance to be correct is 25%
if c is correct, the chance to be correct is 25%
Let P(a/d) to be the possibility of a/d is the correct answer
P(b) to be the possibility of b is the correct answer
P(c) to be the possibility of c is the correct answer
and P(total) to be the possibility of getting the correct answer
Then we have
P(total) = P(a/d) * 50% + P(b) * 25% + (1-P(a/d)-P(b)) * 25%
= P(a/d)*0.5 + P(b)*0.25 + 0.25 - P(a/d)*0.25 - P(b)*0.25
= P(a/d)*0.25 + 0.25
Since one of the answers is correct, P(total) would have value of 25%,
50%
or 60%.
if P(total) = 0.25, we get P(a/d) = 0, which means a, d is not the
correct
answer, which is a conflict.
if P(total) = 0.5, we get P(a/d) = 1, which means only a, d can be the
correct answer, which is also a conflict (since P(total)=0.5 means b is
the
correct answer)
if P(total) = 0.6, we get P(a/d) = 1.4, which is not possible.
Therefore this question has no answer.
However, if either b or c is in the range of (0.25, 0.5), then we can
possibly get a correct answer based on P(a/b).
For example, if choice b is 45%, c is something else (not 25% or 45%).
Then
for P(total) = 0.45, we get P(a/d) = 0.8. In that case, as long as a/d
has
80% chance to be the correct answer, the possibility that we pick the
correct answer will be exactly 45%. Since
P(total) = P(a/d)*0.5 + P(b)*0.25 + P(c)*.025
= P(a/d)*0.5 + (P(b)+P(c)) * 0.25
= 0.8 * 0.5 + 0.2 * 0.25
= 0.45
#
g*a
11 楼
Define event space S1 as the collections of choosing one option.
S1={A,B,C,D}
define event space S2 as the all possible correct answer
S2={a1,a2,a3}(any numbers are fine. Here based on the question a1=0.25, a2=0
.5, a3=0.6)
S1US2={Aa1,Aa2,Aa3,Ba1,Ba2,Ba3,Ca1,Ca2,Ca3,Da1,Da2,Da3}=the collection of
events that the status of your choice
Within all those 12 events, you are making correct choice in 3 events
Aa1,Ba2,Ca3,Da1
So the probability of making correct choice is 4/12=1/3
S1={A,B,C,D}
define event space S2 as the all possible correct answer
S2={a1,a2,a3}(any numbers are fine. Here based on the question a1=0.25, a2=0
.5, a3=0.6)
S1US2={Aa1,Aa2,Aa3,Ba1,Ba2,Ba3,Ca1,Ca2,Ca3,Da1,Da2,Da3}=the collection of
events that the status of your choice
Within all those 12 events, you are making correct choice in 3 events
Aa1,Ba2,Ca3,Da1
So the probability of making correct choice is 4/12=1/3
l*y
12 楼
首先要假设有一个确定的0到1 之间的数 来使得"be correct"有意义。
0 is a consistant answer.
你只要给出正确答案, 没人说这是一道选择题。 http://i.imgur.com/qvzU4.jpg
0 is a consistant answer.
你只要给出正确答案, 没人说这是一道选择题。 http://i.imgur.com/qvzU4.jpg
a*r
13 楼
answer C should be 0%
s*s
14 楼
有3个不同的答案,随机选的话答对的概率肯定小于50%
没一个对
没一个对
s*h
16 楼
Wrong. If there is a correct answer, the value of answer is not r.v. hence
can say "probability that b is correct answer."
actually, there is no correct answer, can be proved easily by contradiction.
【在 b*****n 的大作中提到】![](/moin_static193/solenoid/img/up.png)
: Suppose we randomly pick a, b, c, and d, then
: if a/d is correct, the chance to be correct is 50%
: if b is correct, the chance to be correct is 25%
: if c is correct, the chance to be correct is 25%
: Let P(a/d) to be the possibility of a/d is the correct answer
: P(b) to be the possibility of b is the correct answer
: P(c) to be the possibility of c is the correct answer
: and P(total) to be the possibility of getting the correct answer
: Then we have
: P(total) = P(a/d) * 50% + P(b) * 25% + (1-P(a/d)-P(b)) * 25%
can say "probability that b is correct answer."
actually, there is no correct answer, can be proved easily by contradiction.
【在 b*****n 的大作中提到】
![](/moin_static193/solenoid/img/up.png)
: Suppose we randomly pick a, b, c, and d, then
: if a/d is correct, the chance to be correct is 50%
: if b is correct, the chance to be correct is 25%
: if c is correct, the chance to be correct is 25%
: Let P(a/d) to be the possibility of a/d is the correct answer
: P(b) to be the possibility of b is the correct answer
: P(c) to be the possibility of c is the correct answer
: and P(total) to be the possibility of getting the correct answer
: Then we have
: P(total) = P(a/d) * 50% + P(b) * 25% + (1-P(a/d)-P(b)) * 25%
w*n
20 楼
选任何一个对的概率都是50%
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