To find the cost per ounce for the 40 oz jar, divide the price by the number of ounces: $5.25/40 oz = $0.13 per oz.
To find the cost per ounce for the 15 oz jar, divide the price by the number of ounces: $2.10/15 oz = $0.14 per oz.
Therefore, the 40 oz jar is the better deal because it has a lower cost per ounce.