Question

how many ways mahesh can select a coin from 81 coins in which 80 are similar ones

Answer 1

As 80coins are same we can select 1 coin from them in 1 way
or we can select 1 coin from the remaining 1 in 1 way
so total ways =1+1
=2

Answer 2

This is where probability applies. The probability of choosing one coin out of the 81 coins is 1 out of 81. therefore the probability of choosing 81 coins in which 80 are similar will be 1/81x80..since there is only one chance of choosing a single coin at every turn.

vic