two ways to do it.
1
if we decrease 10%, then we'll have the 90% of the original, so we have:
= 680(90%)
= 680(90/100)
= 612
then 612 is 680 decreased by 10%
2
what is the 10% of 680, call it y?, then reduce it from 680
y = 10%(680) = (10/100)(680) = 68
So, to decrease 680 by 10%, we subtract 680 - 68 = 612