Question

mickey used these calculations to find how much he would spend on 7 cartons of eggs, if 12 cartons of eggs cost $22.20. describe his error.
\frac{12 \text{ cartons}(-22.20)}{\\$22.20(-22.20)}

unit price = $0.54
$0.54(7) = $3.78

Explanation:

Step1: Recall Unit Price Formula

To find the unit price (price per carton), we use the formula: Unit Price = $\frac{\text{Total Cost}}{\text{Number of Cartons}}$. So it should be $\frac{\$22.20}{12 \text{ cartons}}$, not what Mickey did.

Step2: Analyze Mickey's Error

Mickey incorrectly set up the ratio. He divided the number of cartons by the cost and also multiplied by -22.20 (which is unnecessary and wrong). The correct way is to divide total cost by number of cartons to get unit price. Let's calculate correct unit price: $\frac{22.20}{12} = 1.85$ dollars per carton. Then for 7 cartons, it's $1.85\times7 = 12.95$ dollars. Mickey's error was in the unit price calculation: he should divide total cost by number of cartons, not number of cartons by total cost (and the negative operation is irrelevant here).

Answer:

Mickey's error was in calculating the unit price. He should divide the total cost (\$22.20) by the number of cartons (12) to find the unit price, but instead he incorrectly divided the number of cartons by the total cost (and used an irrelevant negative operation). The correct unit price is $\frac{22.20}{12}=\$1.85$ per carton, not \$0.54.