Given :
A carton of 12 eggs or a carton of 18 eggs was the better buy. 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.
To Find :
What was her first error.
Solution :
Her first error is to find Unit price of egg in each carton.
To find, unit price we should divide total amount by number of units :
Unit price for carton of 12 eggs, $ (2.39)/12 = $0.199 .
Hence, this is the required solution.