Make a set of numbers that use all the digits from 1 to 9, once and
once only. Add them up. The result is divisible by 9. Add each of
the digits in the new number. What is their sum? Now try some other
possibilities for yourself!
How many noughts are at the end of these giant numbers?
Stage: 3 and 4 Challenge Level:
To help you get started on this very challenging problem, Alison made a series of videos showing some ways to work on this problem. Perhaps after watching each video you could have another go at solving the problem for yourself before looking to see what Alison does next.
In this video, Alison outlines the problem and starts thinking how to get started.
In this video, Alison multiplies and divides to try to get close to the solution.
In this video, Alison restates the problem in a different way.
In this video, Alison thinks about factors.
In this video, Alison finds a representation that helps.
In this video, Alison considers the units digit.
In the final video, Alison tries some more combinations and finds one that works!
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. More information on many of our other activities
can be found here.