Question

At the student store, pencils are sold in either packs of three or packs of eight.

Without opening any packages, which numbers of pencils is it possible to buy?
Which numbers are impossible?

Answer 1

4, 7, 5, 10, 13, .......

Explanation:

the only numbers that are impossible to get are the non-multiples of 3 and 8

and the numbers that 8 and 3 do not add up to and the multiples of 8 and 3 do not add up to