You add three multiples of a number together. Will the sum be a multiple of the number? Explain why or why not?

kkkk

of course it is

let the 3 multiples of the same number k be
ak, bk, and ck
sum= ak + bk + ck
= k(a+b+c) which is a multiple of k

e.g 15, 24, and 60 are all multiples of 3, that is, each is divisible by 3
sum = 15+24+60 = 99 and of course 99 is a multiple of 3
99 = 3(33)