Bryan bought some markers at $2 each. He later sold them to his customers at $5 each. For customers who bought four markers were given another marker for free. The customers bought either one or four markers. Bryan gave away 130 free markers and collected a total of $1360 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 5 markers each
Number	1 u	1 u - 650	650
Value	$2	$5	$5
Total Value	2 u	5 u - $3250	$2600

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

Number of markers that each customer would get if they bought four markers each and got 1 marker free
= 4 + 1
= 5

Total number of markers for customers who each bought four markers 
= 5 x 130
= 650

Number of markers for customers who each bought 1 marker = 1 u - 650

Total amount collected from customers who bought 1 marker each
= 5 x (1 u - 650)
= 5 u - 3250

Total amount collected from customers who bought four markers each
= 130 x 4 x 5
= $2600

Total amount collected from all the customers
= 5 u - 3250 + 2600
= 5 u - 650

Bryan collected a total of $1360 more than what he had paid for.

5 u - 650 = 2 u + 1360
5 u - 2 u = 1360 + 650
3 u = 2010

1 u = 2010 ÷ 3 = 670

Number of customers who bought just one marker
= 1 u - 650
= 670 - 650
= 20

Answer(s): 20