you'll get better with time at doing these in your head..... say you have a number like 71
You might think 8 as a sq rt 8*8 = 64
SO the answer is greater than 8....hmmmm Maybe 9
9*9 = 81 Well 9 is too big so the answer is between 8 and 9
Guess an estimate maybe 8.4
If you have a calculator you will find 8.4 x 8.4 = 70.6 pretty close for an 'estimate'
