Question

A bag contains twenty Rs $5$ coins, fifty Rs $2$ coins, and thirty Re $1$ coins. If it is equally likely that one of the coins will fall down when the bag is turned upside down, what is the probability that the coin will not be a Rs $2$ coin?

Answer 1

We have,

Total number of coins $=20+50+30=100$

So, the total possible outcomes $=100=n\left(S\right)$

Number of favourable outcomes for not a Rs $2$ coins = number of favourable outcomes for Re $1$ or Rs $5$ coins $=30+20=50=n\left(E\right)$

Hence, probability (not Rs $2$ coin) $=n\left(E\right)/n\left(S\right)=\frac{1}{2}$