Zane bought some pencils at $4 each. He later sold them to his customers at $7 each. For customers who bought two pencils were given another pencil for free. The customers bought either one or two pencils. Zane gave away 100 free pencils and collected a total of $650 more than what he had paid for. How many customers bought just one pencil each?

	Pencils sold	Pencils given to customers who got 1 pencil each	Pencils given to customers who got 3 pencils each
Number	1 u	1 u - 300	300
Value	$4	$7	$7
Total Value	4 u	7 u - $2100	$1400

Since 100 pencils were given free, there were 100 customers who bought two pencils each.

Number of pencils that each customer would get if they bought two pencils each and got 1 pencil free
= 2 + 1
= 3

Total number of pencils for customers who each bought two pencils 
= 3 x 100
= 300

Number of pencils for customers who each bought 1 pencil = 1 u - 300

Total amount collected from customers who bought 1 pencil each
= 7 x (1 u - 300)
= 7 u - 2100

Total amount collected from customers who bought two pencils each
= 100 x 2 x 7
= $1400

Total amount collected from all the customers
= 7 u - 2100 + 1400
= 7 u - 700

Zane collected a total of $650 more than what he had paid for.

7 u - 700 = 4 u + 650
7 u - 4 u = 650 + 700
3 u = 1350

1 u = 1350 ÷ 3 = 450

Number of customers who bought just one pencil
= 1 u - 300
= 450 - 300
= 150

Answer(s): 150