Special Sums

Imagine you have four bags containing a large number of 1s, 4s, 7s and 10s.

You can choose numbers from the bags and add them to make different totals. You don’t have to use numbers from every bag, and there will always be as many of each number as you need.

Choose some sets of 3 numbers and add them together.

What is special about your answers?
Can you explain what you’ve noticed?

Click here to download the SPECIAL SUMS worksheet.

Click here to download Notes for Teachers.

This problem is adapted from the NRICH task What Numbers Can We Make with permission of the University of Cambridge. All rights reserved.