Peter bought some markers at $4 each. He later sold them to his customers at $7 each. For customers who bought three markers were given another marker for free. The customers bought either one or three markers. Peter gave away 140 free markers and collected a total of $1030 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 4 markers each
Number	1 u	1 u - 560	560
Value	$4	$7	$7
Total Value	4 u	7 u - $3920	$2940

Since 140 markers were given free, there were 140 customers who bought three markers each.

Number of markers that each customer would get if they bought three markers each and got 1 marker free
= 3 + 1
= 4

Total number of markers for customers who each bought three markers 
= 4 x 140
= 560

Number of markers for customers who each bought 1 marker = 1 u - 560

Total amount collected from customers who bought 1 marker each
= 7 x (1 u - 560)
= 7 u - 3920

Total amount collected from customers who bought three markers each
= 140 x 3 x 7
= $2940

Total amount collected from all the customers
= 7 u - 3920 + 2940
= 7 u - 980

Peter collected a total of $1030 more than what he had paid for.

7 u - 980 = 4 u + 1030
7 u - 4 u = 1030 + 980
3 u = 2010

1 u = 2010 ÷ 3 = 670

Number of customers who bought just one marker
= 1 u - 560
= 670 - 560
= 110

Answer(s): 110