Three persons i.e. ‘M’, ‘N’ and ‘O’, are given

Solution

Probability of ‘M’ solving the puzzle = 7/10
Therefore, probability of ‘M’ not solving the puzzle = 1 – (7/10) = 3/10
Probability of ‘N’ solving the puzzle = 3/5
Therefore, probability of ‘N’ not solving the puzzle = 1 – (3/5) = 2/5
Probability of ‘O’ solving the puzzle = 1/2
Therefore, probability of ‘O’ not solving the puzzle = 1 – (1/2) = 1/2
Therefore, required probability = {(3/10) × (3/5) × (1/2)} + {(7/10) × (2/5) × (1/2)} + {(7/10) × (3/5) × (1/2)}
= (9/100) + (14/100) + (21/100) = 44/100 = 11/25