A grocery store sells four different jars of peanut butter. Determine which is the best​ buy, based on the cost per unit.

12 ounces for ​$1.39 22 ounces for ​$2.38
30 ounces for ​$3.15 36 ounces for ​$3.46

To determine the cost per ounce for each jar of peanut butter, divide the total cost by the number of ounces in the jar.

For the first jar: $1.39 / 12 ounces = $0.116 per ounce
For the second jar: $2.38 / 22 ounces = $0.108 per ounce
For the third jar: $3.15 / 30 ounces = $0.105 per ounce
For the fourth jar: $3.46 / 36 ounces = $0.096 per ounce

Based on cost per unit, the fourth jar of peanut butter (36 ounces for $3.46) is the best buy.