Answer:
15 ounce bag is cheaper per ounce than 9.75 ounce bag.
Step-by-step explanation:
For this problem, you should simply take the cost divide by the size for each to find the price per ounce.
$3.98 / 15oz == $0.265 per ounce
$2.98 / 9.75oz == $0.306 per ounce
Note that the 15 oz bag is a better price per ounce than the 9.75 oz bag.
As to what bag you should buy, that really should depend on more factors than just what's best per ounce. For instance, are you really hungry enough for 15 ounces of doritos, or will 9.75 do just fine? Also, do you even have the extra dollar it would cost to buy the bigger bag? Just some stuff to think about.
Cheers.