Ethan bought some pencils at $2 each. He later sold them to his customers at $7 each. For customers who bought three pencils were given another pencil for free. The customers bought either one or three pencils. Ethan gave away 180 free pencils and collected a total of $2440 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 4 pencils each
Number	1 u	1 u - 720	720
Value	$2	$7	$7
Total Value	2 u	7 u - $5040	$3780

Since 180 pencils were given free, there were 180 customers who bought three pencils each.

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

Total number of pencils for customers who each bought three pencils 
= 4 x 180
= 720

Number of pencils for customers who each bought 1 pencil = 1 u - 720

Total amount collected from customers who bought 1 pencil each
= 7 x (1 u - 720)
= 7 u - 5040

Total amount collected from customers who bought three pencils each
= 180 x 3 x 7
= $3780

Total amount collected from all the customers
= 7 u - 5040 + 3780
= 7 u - 1260

Ethan collected a total of $2440 more than what he had paid for.

7 u - 1260 = 2 u + 2440
7 u - 2 u = 2440 + 1260
5 u = 3700

1 u = 3700 ÷ 5 = 740

Number of customers who bought just one pencil
= 1 u - 720
= 740 - 720
= 20

Answer(s): 20