Heres a good math tip. If you are squaring a number that ends in 5, like 25 or 65, then just multiply the tens digit by the next consecutive one, ie for 25 -> 2x3 for 45 -> 4x5 and put a 25 on the end of the answer. It works from 5 to 95 like this.
05 x 05 = (0*1)(stuck onto)25 -> 025
15 x 15 = (1*2)(stuck onto)25 -> 225
25 x 25 = (2*3)(stuck onto)25 -> 625
35 x 35 = (3*4)(stuck onto)25 -> 1225
etc.