7/20= how would i figure that answer if i didn't have no calculator?

You don't need a calculator for everything! 
Think about it this way: We know 20=2x10, so 7 divided by 20=7/(2x10), which we can solve as 7/10/2. 7/10=0.7, then all we have to do is divide 0.7 by 2. Well we know 0.6/2 is 0.3, so 0.7 divided by 2 is 0.35. 
So 0.35 is your answer :)