Zane bought some markers at $4 each. He later sold them to his customers at $9 each. For customers who bought two markers were given another marker for free. The customers bought either one or two markers. Zane gave away 110 free markers and collected a total of $1710 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	$4	$9	$9
Total Value	4 u	9 u - $2970	$1980

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
= 9 x (1 u - 330)
= 9 u - 2970

Total amount collected from customers who bought two markers each
= 110 x 2 x 9
= $1980

Total amount collected from all the customers
= 9 u - 2970 + 1980
= 9 u - 990

Zane collected a total of $1710 more than what he had paid for.

9 u - 990 = 4 u + 1710
9 u - 4 u = 1710 + 990
5 u = 2700

1 u = 2700 ÷ 5 = 540

Number of customers who bought just one marker
= 1 u - 330
= 540 - 330
= 210

Answer(s): 210