1) Gathering data from the question
A -14 ounce $4.2
B -12 ounce $3.9
2) To answer which one is better we need to know how many ounces, the family has per weak?
3) Let's calculate how much is one ounce in a Cereal A, using a rule of three
14 ounces - 4.20
1 ounce -- x
14x = 4.20 Dividing by 14:
x= $0.3 1 ounce
Cereal B
12 ounces ----3.90
1 ounce ------y
12y=3.90
y= $0.325
So the (not much ) cheaper option is choosing cereal B
4) Now, what If spending $3.97 for the 14 oz box of cereal OR $4.23 for the 16 oz box of cereal?
$3.97 --------14 oz
z --------- 1
14z =3.97
z= $0.28
$4.23 -----16
k -------------1
16k ----$4.23
k=$0.26
Finally, the best option is to buy a 16 oz box by $4.23 because by doing this you're paying the best price per ounce of Cereal.