In the first week of last month, Company X realized an average wholesale profit of $7140 per day from the sale of q units of Product Y. Which of the following CANNOT be the difference between Product Y’s sale price and cost per unit?
Choices: A) $3 B) $4 C) $7 D) $13 E) $51
The key operator that everyone seems to have missed is the average. The average profit of $7140 per day is equivalent to a total profit of $49980 for the whole week.   Therefore, the difference between sale price and cost per unit is equal to $49980, which is divisible by all of the answer choices, except for 13.   So, $13 is the answer.
<result>D</result>
In the first week of last month, Company X realized an average wholesale profit of $7140 per day from the sale of q units of Product Y. Which of the following CANNOT be the difference between Product Y’s sale price and cost per unit?