A couple has two children. Find the probability that both the children are (i) males, if it is known that at least one of the children is male. (ii) females, if it is known that the elder child is a female.

Explanation

If a couple has two children, then the sample space is
`S={(b,b),(b,g),(g,b),(g,g)}`

(i) Let E and F respectively denote the events that both children
are males and at least one of the children is a male.

`∴E∩F={(b,b)}⇒P(E∩F)=1/4`

`P(E)=1/4`

`P(F)=3/4`

`⇒P(E∣F)=P(F)P(E∩F)​=(1/4)/(3/4)`

`=1/3`


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