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.

12 cartons(÷22.20)
$22.20(÷22.20)

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

1 answer

Mickey's error lies in the way he calculated the unit price and how he treated the division in his initial steps. Let's break it down:

  1. Misinterpretation of Division: Mickey used the division operation incorrectly. When he wrote "12 cartons(÷22.20)" and then "$22.20(÷22.20)", he did not arrive at the correct unit price of the eggs. Instead, he should have divided the total cost by the number of cartons to find the price per carton.

  2. Correct Calculation of Unit Price:

    • The unit price should be calculated as: \[ \text{Unit Price} = \frac{\text{Total Cost}}{\text{Number of Cartons}} = \frac{22.20}{12} \]
    • This calculation results in: \[ \text{Unit Price} = 1.85 , (\text{approximately}) \]
  3. Calculating the Total Cost for 7 Cartons:

    • After finding the correct unit price of approximately $1.85 per carton, he would then multiply this unit price by 7 to find out how much he would spend: \[ \text{Total Cost for 7 Cartons} = 1.85 \times 7 \approx 12.95 \]
  4. Mickey's Incorrect Total: Mickey incorrectly arrived at a unit price of $0.54 and then calculated the cost for 7 cartons as $3.78. These results are wrong due to the miscalculation of the unit price.

In summary, Mickey's error was in the method he used to calculate the unit price, leading to a chain of incorrect subsequent calculations.