Question

How can you explain that 3/5 is not equivalent to 18/20

Answer 1

3/5= .6

and 

18/20= .9

that means .6 is not equal to .9

Answer 2

3/5 is not equivalent to 18/20 because if you convert 3/5 into twentieths (numerator times 4, denominator times 4), you get 12/20, which is obviously not equivalent to 18/20.