dse 2009

[MI]

18. You've been told that a family has two children and one of these is
a daughter. What is the probability that the other child is also a daughter?
a) 1/2
b) 1/3
c) 1/4
d) 3/

i am getting a) 1/2  as my answer.....

is it correct?

[Sumit]

HI MI,
Right answer is 1/3..... Basically in this question you need to find conditional probability i.e P(that the other child is also a daughter given that one of the child is a daughter)...
S={BB, DD, BD, DB}
Let A=One of the child is Daughter.
B=other child is also daughter=both the child is daughter...

A={DD, BD, DB}, B={DD}..P(A)=3/4 & P(B)=1/4. P(BA)=1/4

So, P(B/A)=P(BA)/P(A)=1/3..

[cx]

and if u dont want to apply the formulae then work on the restricted sample space! dd out of ds sd dd which will give u ans! either u work on restricted sample space or apply the formulae on orig sample space!

[MI]

Thanks :D