manOnFire wrote:

bmwhype2 wrote:

1.

Prob that Sally will not win = 4/5

Prob that Jeny will not win = 4/5

Hence 4/5 * 4/5 = 16/25

correct?

Can someone explain the flaw here?

5 women are in a race.

What is the probability that Sally and Jenny both will not win the race?

Say S,J, X1,X2,X5 are in the race.. [ assuming the only one person will win the race out of 5 with equal probablity]

All these events[Winning S, Winning J, Winning X1.] are "mutually exclusive" --> Out comes are not common.

P(S) = 1/5

P(J) =1/5

P(X1)=1/5

P(X2)=1/5

P(X3)=1/5

probability of either one of them winning hte race

= P(S or J or X1 or X2 or X3) =P(S) +P(J)+P(X1)+P(X2)+P(X3) =1

probability that Sally and Jenny both will not win the race = probability that either one of X1 or X2 or X2 them win the race = P(X1)+P(X2)+P(X3) =1/5+1/5+1/5=3/5

check the below link, it may be useful for you.

http://www.regentsprep.org/regents/math/mutual/Lmutual.htm _________________

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