The change from 3/4 to 4/10 is found by obtaining and applying the LCD:
15/20 to 8/20 is a negative change, and the amount of the change was -7/20.
We compare this result to the original value, 15/20, to obtain the percentage change in the fraction:
-7/20
----------- = -7/15 = -0.467 => -46.7%
15/20
