Q.

Let 5 digit numbers be constructed using the digits 0, 2, 3, 4, 7, 9 with repetition allowed, and are arranged in ascending order with serial numbers. Then the serial number of the number 42923 is _______ .              [2023]


Ans.

(2997)

Number starting with 2 and 3 = 2×64

Number starting with 40 = 63

Number starting with 420, 422, 423, 424, 427 = 5×62

Similarly, number starting with 4290 = 6

Total=2×64+63+5×62+6+3=2997