Can you work out the arrangement of the digits in the square so
that the given products are correct? The numbers 1 - 9 may be used
once and once only.
Stage: 2 Challenge Level:
Do both cogs turn in the same direction? With two cogs that have five teeth, will the marked tooth on one cog eventually fit in every gap of the other cog as they turn? Why or why not? What happens if you pick a cog with five teeth and a cog with 6 teeth?
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.