Abby can buy an 8-pound bag of dog food for $7.40 or a 4-pound bag of the same dog food for $5.38.which is better to buy? how do you know?

Okay, so we know that if Abby were to go for that first option, she would buy that 8-pound bag for $7.40. But if she were to go for the second option, well, we would have to find out how much an 8-pound bag would cost there too, to see which one is a lower price, even though it's for the same amount of pounds.

To find how much the second deal would cost for 8-pounds, we would have to put it in as  and multiply both the numerator and the denominator by 2, because 4 and 2 make 8, and if we multiply the numerator by 2, we'd have to multiply the denominator by 2. So if we were to multiply 5.38 by 2, we would end up with 10.76.

OPTION ONE : 8-pound bag, for $7.40
OPTION TWO : two 4-pound bags (same as 8-pounds) for $10.76

The first option would be a better deal, because it's the same amount of pounds for a lesser price.