Cody bought some staplers at $4 each. He later sold them to his customers at $7 each. For customers who bought two staplers were given another stapler for free. The customers bought either one or two staplers. Cody gave away 100 free staplers and collected a total of $1370 more than what he had paid for. How many customers bought just one stapler each?

	Staplers sold	Staplers given to customers who got 1 stapler each	Staplers given to customers who got 3 staplers each
Number	1 u	1 u - 300	300
Value	$4	$7	$7
Total Value	4 u	7 u - $2100	$1400

Since 100 staplers were given free, there were 100 customers who bought two staplers each.

Number of staplers that each customer would get if they bought two staplers each and got 1 stapler free
= 2 + 1
= 3

Total number of staplers for customers who each bought two staplers 
= 3 x 100
= 300

Number of staplers for customers who each bought 1 stapler = 1 u - 300

Total amount collected from customers who bought 1 stapler each
= 7 x (1 u - 300)
= 7 u - 2100

Total amount collected from customers who bought two staplers each
= 100 x 2 x 7
= $1400

Total amount collected from all the customers
= 7 u - 2100 + 1400
= 7 u - 700

Cody collected a total of $1370 more than what he had paid for.

7 u - 700 = 4 u + 1370
7 u - 4 u = 1370 + 700
3 u = 2070

1 u = 2070 ÷ 3 = 690

Number of customers who bought just one stapler
= 1 u - 300
= 690 - 300
= 390

Answer(s): 390