EDIT: I misread the task, i meant how do i figure out 0.05^2 without a calculator.

If you happen to know, off the top of your head, that sqrt(5) is 2.236 (3dp) then you could write 0.05 = 5/100 which, on taking the sqr root would be 2.236/10 = 0.2236.

.05^2

Note    .05  =    5 / 100   =  1 / 20

So

.05^2  =  (5/100)^2  =  (1/20)^2   = (1/20) (1/20)   = 1  / 400

Also

.05

.05

___

.0025

These two answers are equivalent