Henry bought some markers at $4 each. He later sold them to his customers at $6 each. For customers who bought two markers were given another marker for free. The customers bought either one or two markers. Henry gave away 220 free markers and collected a total of $160 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 - 660	660
Value	$4	$6	$6
Total Value	4 u	6 u - $3960	$2640

Since 220 markers were given free, there were 220 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 220
= 660

Number of markers for customers who each bought 1 marker = 1 u - 660

Total amount collected from customers who bought 1 marker each
= 6 x (1 u - 660)
= 6 u - 3960

Total amount collected from customers who bought two markers each
= 220 x 2 x 6
= $2640

Total amount collected from all the customers
= 6 u - 3960 + 2640
= 6 u - 1320

Henry collected a total of $160 more than what he had paid for.

6 u - 1320 = 4 u + 160
6 u - 4 u = 160 + 1320
2 u = 1480

1 u = 1480 ÷ 2 = 740

Number of customers who bought just one marker
= 1 u - 660
= 740 - 660
= 80

Answer(s): 80