Prove that 3 times the sum of 3 squares is the sum of 4 squares.
Rather easier, can you prove that twice the sum of two squares
always gives the sum of two squares?
Crack this code which depends on taking pairs of letters and using
two simultaneous relations and modulus arithmetic to encode the
Given the mean and standard deviation of a set of marks, what is
the greatest number of candidates who could have scored 100%?