Which is better buy? 5 lb of flour for $0.90 or
8 lb for $1.25

Well let’s see if there’s a least common multiple of 5 and 8. Since 40 is the least common mult. We will multiply 40 x .90 and 40 x 1.25 . 40x.90 is 36 while 40x1.25 is 50. It’s better to buy eight pounds for 1.25!