You may also like

problem icon

Counting Factors

Is there an efficient way to work out how many factors a large number has?

problem icon

Summing Consecutive Numbers

15 = 7 + 8 and 10 = 1 + 2 + 3 + 4. Can you say which numbers can be expressed as the sum of two or more consecutive integers?

problem icon

Helen's Conjecture

Helen made the conjecture that "every multiple of six has more factors than the two numbers either side of it". Is this conjecture true?

Please Explain

Age 11 to 14 Challenge Level:

Take a look at the two multiplications below. What do you notice?

$32 \times 46 = 1472$
$23 \times 64 = 1472$

The digits in this multiplication have been reversed, and the answer has stayed the same!

Is this surprising? Can you find other examples where this happens?

What do you notice about the pairs of two digit numbers that produce this special result?


The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice.
Copyright © 1997 - 2020. University of Cambridge. All rights reserved.
NRICH is part of the family of activities in the Millennium Mathematics Project.