Nikki used the calculations shown to determine whether a carton of 12 eggs or a carton of 18 eggs was the better buy.

Question

A carton of 12 eggs cost $2.39, and a carton of 18 eggs cost $3.39.
Unit price of the 12-egg carton = ($2.39)(12 eggs) = $28.68 per egg
Unit price of the 18-egg carton = ($3.39)(18 eggs) = $61.02 per egg
The 12-egg carton has the lower unit cost, so it is the better buy.

What was her first error?
She should have divided the cost of the carton by the number of eggs to find the price per egg.
She should have divided the number of eggs by the cost of the carton to find the price per egg.
She made a computational error when multiplying to find the unit price of the two cartons.
She made an error in choosing the eggs with the lower unit cost to be the better buy.

Answer 1

Nikki's first error was:

She should have divided the cost of the carton by the number of eggs to find the price per egg.

To correctly calculate the unit price, she should use the formula:

\[ \text{Unit price} = \frac{\text{Cost of carton}}{\text{Number of eggs}} \]

For the 12-egg carton: \[ \text{Unit price} = \frac{2.39}{12} \approx 0.1992 \text{ per egg} \]

For the 18-egg carton: \[ \text{Unit price} = \frac{3.39}{18} \approx 0.1883 \text{ per egg} \]

By comparing these unit prices, you can determine the better buy based on the lower price per egg.