Answer:
The price was reduced by 25%
Explanation:
Not sure how to go step by step on this, because it's kinda obvious once you think about it a bit. You need to find what percent of 40 that 10 equals (if that makes sense). So really it's just what percent of 40 equals 10? and since 10 is one fourth of forty, 1/4, then you convert that to percent: 25% (sorry if this made no sense, i'm not very good at explaining things)