use bayes thm
ans = 1/3
a letter is known to have come from either TATANAGAR or CALCUTTA on d envelope just 2 consecutive letters TA r visible d probability dat d letter has come from calcutta is?
its soln is given in TMH but i dont understand can ne1 give d soln plz
it is a type of permutation and combination type of question. and then only u can apply Baye's theorem
prob of letter being from cal. or tata. is 1/2
u can select 2 consecutive letters from calcutta in 7 ways
( CA or AL or LC or CU or UT or TT or TA )
nd frm TATANAGAR in 8 ways
out of this, TA from calcutta in 1 way
and from tatanagar in 2 ways
Now use Baye's theorem ....
1/2 * 1/7 / ( 1/2 * 1/7 + 1/2 * 2/8 )
= 4/ 11