"A piggy bank comprises 5-rupee coins, 10-rupee coins,

Solution

ATQ, Let the number of 10 rupees coins in the piggy bank be 'p'. So, the number of 5 rupeees coins in the piggy bank = 0.7p And the number of 20 rupees coins in the piggy bank = 0.70/1.75 = 0.4p So, the total number of coins in the piggy bank = p + 0.7p + 0.4p = 2.1p So, the probability that a 5 rupees coins and a 10 rupees coins are drawn = ^pC1 × ^0.7pC1/ ^2.1pC2 = 1/3 (2p × 0.7p) / {2.1p (2.1p - 1) } = 1/3  2.1p - 1 = 2p 0.1p = 1, p = 10 So, the total number of coins in the piggy bank = 2.1 × 10 = 21