10th CanMO 1978 Problem A square has tens digit 7. What is the units digit?
Suppose the unsquared number has tens digit a and units digit b. The carry from b 2 must be odd (since 7 is odd), so b = 4 or 6. In either case the units digit of the square is 6. An example is 26 2 = 576. 10th CanMO 1978 © John Scholes jscholes@kalva.demon.co.uk 10 June 2002