Owen bought some markers at $5 each. He later sold them to his customers at $10 each. For customers who bought two markers were given another marker for free. The customers bought either one or two markers. Owen gave away 130 free markers and collected a total of $2000 more than what he had paid for. How many customers bought just one marker each?

	Markers sold	Markers given to customers who got 1 marker each	Markers given to customers who got 3 markers each
Number	1 u	1 u - 390	390
Value	$5	$10	$10
Total Value	5 u	10 u - $3900	$2600

Since 130 markers were given free, there were 130 customers who bought two markers each.

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

Total number of markers for customers who each bought two markers 
= 3 x 130
= 390

Number of markers for customers who each bought 1 marker = 1 u - 390

Total amount collected from customers who bought 1 marker each
= 10 x (1 u - 390)
= 10 u - 3900

Total amount collected from customers who bought two markers each
= 130 x 2 x 10
= $2600

Total amount collected from all the customers
= 10 u - 3900 + 2600
= 10 u - 1300

Owen collected a total of $2000 more than what he had paid for.

10 u - 1300 = 5 u + 2000
10 u - 5 u = 2000 + 1300
5 u = 3300

1 u = 3300 ÷ 5 = 660

Number of customers who bought just one marker
= 1 u - 390
= 660 - 390
= 270

Answer(s): 270