Let below are the two given events,
`A = `A prime number appears on second die.
There are `3` numbers `(2,4,6)` that are prime between `1` and `6`.
So, second die can contain any of these three numnbers.
First die can have any of he `6` numbers.
`:. n(A) = 6*3 = 18`
Let `B = `Event that sum of both dice is `7`.
Then, `B = {(2,5),(1,6),(3,4),(4,3),(5,2),(6,1)}`
`:. n(B) = 6`
Now, `(AnnB) = {(2,5),(5,2),(4,3)}`
`=>n(AnnB) = 3`
`:.` Required probability , `P(B/A) = (n(AnnB) )/(n(A)) = 3/18 = 1/6`
