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Solution


Q.

A person forgets his 4-digit ATM pin code. But he remembers that in the code all the digits are different, the greatest digit is 7 and the sum of the first two digits is equal to the sum of the last two digits.Then the maximum number of trials necessary to obtain the correct code is _____ .          [2023]

Ans.

(72)

Sum of first two digits

Sum of last two digits = α

Case–I : α = 7

2 × 12 = 24 ways.

2 × 8 ways = 16 ways

2 × 4 ways = 8 ways

Total ways = 24 + 16 + 16 + 8 + 8 = 72