Question

how many three digit numbers can be made using only the digits {1, 2, 4, 6, 8, 9} repetition is allowed

Answer 1

56

Explanation:

Given data:

{1 ,2 ,4, 6, 8, 9}

Formula for combinations is used since the order does not matter and repetition is allowed.

nCr = (n + r -1) /(r! * (n-1)!) where n is the total number of items and r is the items to be picked

6C3 = (6 + 3 - 1)! /(3! * (6 -1)!

6C3 = 8!/(3! *5!) Simplifying the factorials)

6C3 = 40320/(6*120)

6C3 = 40320/720

6C3 = 56