You may also like

Double Time

Crack this code which depends on taking pairs of letters and using two simultaneous relations and modulus arithmetic to encode the message.

Modular Fractions

We only need 7 numbers for modulus (or clock) arithmetic mod 7 including working with fractions. Explore how to divide numbers and write fractions in modulus arithemtic.

Old Nuts

In turn 4 people throw away three nuts from a pile and hide a quarter of the remainder finally leaving a multiple of 4 nuts. How many nuts were at the start?


Age 16 to 18 Challenge Level:

Try to be systematic. How can you narrow down the cases to be tested?


If the last digit of a square number is 9 what can you say about the number?

Can you write down an expression for a number using its digits and powers of 10?
Possible support


Note: Other problems using modulus arithmetic: Dirisibly Yours , Obviously, Rational Round
An article that explains the basic ideas of modulus arithmetic: Modulus Arithmetic and Solution to Dirisibly Yours.