Question

A piggy bank contains hundred $50p$ coins, fifty $Rs.1$ coins, twenty $Rs.2$ coins and ten $Rs.5$ coins. If it is equally likely that one of the coins will fall out when the bank is turned upside down, what is the probability that the coin (i) will be a $50p$ coin ? (ii) will not be a $Rs.5$ coin?

Answer 1

Total number of coins in the piggy bank $=100+50+20+10=180$

i) Probability ($50p$ coin) $=\frac{\text{number of 50p coins}}{\text{total number of coins}}$ $=\frac{100}{180}$

P($50p$ coin) $=\frac{5}{9}$

ii) Number of $Rs.5$ coins $=10$

Number of coins which are not $Rs.5=170$

Probability (coin not being $Rs.5$) $=\frac{170}{180}=\frac{17}{18}$