If we factorize the expression

We will get

Hope I helped!
I think they are not always the best deal, but most are. Sometimes they are not good if they opponent has a even lower price then them.
1/3 = 8/24
1/8 = 3/24
use 24 since it's the LCM of 8 and 3
8-3/24 = 5/24
-1 as a negative would = X