- #1
Dell
- 590
- 0
in a room there are 3 married couples
somebody guesses which of the men are married to which of the women.
X=number of correct guesses.
find E(x), var(x)
i tried the following
X=0 (no correct guesses)
P(X)=2/3*2/3*2/3=8/27
X=1 (one correct guess)
P(X)=2/3*2/3*1/3=4/27
X=2 (two correct guesses)
P(X)=2/3*1/3*1/3=2/27
X=1 (three correct guesses)
P(X)=1/3*1/3*1/3=1/27
BUT the total
P(X=0) + P(X=1) + P(X=2) + P(X=3) does not come to 1
(8+4+2+1)/27=5/9
where am i going wrong? there are only 3 couples so he could not guess more that 3 correct couples.
the probability of guessing a correct couple is 1 in 3
somebody guesses which of the men are married to which of the women.
X=number of correct guesses.
find E(x), var(x)
i tried the following
X=0 (no correct guesses)
P(X)=2/3*2/3*2/3=8/27
X=1 (one correct guess)
P(X)=2/3*2/3*1/3=4/27
X=2 (two correct guesses)
P(X)=2/3*1/3*1/3=2/27
X=1 (three correct guesses)
P(X)=1/3*1/3*1/3=1/27
BUT the total
P(X=0) + P(X=1) + P(X=2) + P(X=3) does not come to 1
(8+4+2+1)/27=5/9
where am i going wrong? there are only 3 couples so he could not guess more that 3 correct couples.
the probability of guessing a correct couple is 1 in 3