Sean answered 18/20. To convert to percent we multiply by 100: 18/20*100. 20 goes into 100 5 times so we multiply 18 by 5 to get 90%. Another way is to say: what do we multiply numerator and denominator by so that the denominator becomes 100? The answer is 5 so (5*18)/(5*20)=90/100 which is 90%, third answer.