Jenson bought some staplers at $2 each. He later sold them to his customers at $7 each. For customers who bought three staplers were given another stapler for free. The customers bought either one or three staplers. Jenson gave away 110 free staplers and collected a total of $3180 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 4 staplers each
Number	1 u	1 u - 440	440
Value	$2	$7	$7
Total Value	2 u	7 u - $3080	$2310

Since 110 staplers were given free, there were 110 customers who bought three staplers each.

Number of staplers that each customer would get if they bought three staplers each and got 1 stapler free
= 3 + 1
= 4

Total number of staplers for customers who each bought three staplers 
= 4 x 110
= 440

Number of staplers for customers who each bought 1 stapler = 1 u - 440

Total amount collected from customers who bought 1 stapler each
= 7 x (1 u - 440)
= 7 u - 3080

Total amount collected from customers who bought three staplers each
= 110 x 3 x 7
= $2310

Total amount collected from all the customers
= 7 u - 3080 + 2310
= 7 u - 770

Jenson collected a total of $3180 more than what he had paid for.

7 u - 770 = 2 u + 3180
7 u - 2 u = 3180 + 770
5 u = 3950

1 u = 3950 ÷ 5 = 790

Number of customers who bought just one stapler
= 1 u - 440
= 790 - 440
= 350

Answer(s): 350