Mother,Father and Son line up at random for a family picture.E : son on one end, F:Father in middle. Find P(E/F).

Explanation

Suppose A,B,C denote the mother, the father and the son respectively.
Then S ={ABC,ACB,BAC,BCA,CAB,CBA} `rArr` n(S) = 6
E = {CAB,CBA,ABC,BAC}, F={ABC,CAB} `rArr` n(F)=2
Also,`EnnF`={ABC,CAB}`rArr` n`(EnnF)` = 2
therefore`P(EnnF)`=2/6 and P(F) =2/6 `rArr` P(E/F) = `(P(EnnF))/P(F))`=1