First slide

Permutations

Question

A four digit number of distinct digits is formed by using the digits 2, 3, 4, 5, 6, 7, 8. The number of such numbers which are divisible by 25, is

Moderate

A

60
B

40
C

20
D

15

Solution

The number will be divisible by 25 if it ends in 25 or 75.
Therefore, the required number of numbers is
$(^{5} P_{2}) (2) = 40$

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