Jack bought some markers at $6 each. He later sold them to his customers at $11 each. For customers who bought two markers were given another marker for free. The customers bought either one or two markers. Jack gave away 110 free markers and collected a total of $2040 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 - 330	330
Value	$6	$11	$11
Total Value	6 u	11 u - $3630	$2420

Since 110 markers were given free, there were 110 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 110
= 330

Number of markers for customers who each bought 1 marker = 1 u - 330

Total amount collected from customers who bought 1 marker each
= 11 x (1 u - 330)
= 11 u - 3630

Total amount collected from customers who bought two markers each
= 110 x 2 x 11
= $2420

Total amount collected from all the customers
= 11 u - 3630 + 2420
= 11 u - 1210

Jack collected a total of $2040 more than what he had paid for.

11 u - 1210 = 6 u + 2040
11 u - 6 u = 2040 + 1210
5 u = 3250

1 u = 3250 ÷ 5 = 650

Number of customers who bought just one marker
= 1 u - 330
= 650 - 330
= 320

Answer(s): 320