A letter is known to come from the place DELHI,MAHILAPUR,HIMACHAL,HISHAR,MANPUR. Probability that it came from DELHI if post master consider only 2 consequtive letters HI is?



ans-315/787

We have to consider the number of pairs of 2 consecutive letters. By baye's theorem

P =  

Have i made any mistake?

as sboosy pointed it out, its 280 and not 240 in the nr!