Tommy bought some files at $3 each. He later sold them to his customers at $5 each. For customers who bought two files were given another file for free. The customers bought either one or two files. Tommy gave away 200 free files and collected a total of $440 more than what he had paid for. How many customers bought just one file each?

	Files sold	Files given to customers who got 1 file each	Files given to customers who got 3 files each
Number	1 u	1 u - 600	600
Value	$3	$5	$5
Total Value	3 u	5 u - $3000	$2000

Since 200 files were given free, there were 200 customers who bought two files each.

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

Total number of files for customers who each bought two files 
= 3 x 200
= 600

Number of files for customers who each bought 1 file = 1 u - 600

Total amount collected from customers who bought 1 file each
= 5 x (1 u - 600)
= 5 u - 3000

Total amount collected from customers who bought two files each
= 200 x 2 x 5
= $2000

Total amount collected from all the customers
= 5 u - 3000 + 2000
= 5 u - 1000

Tommy collected a total of $440 more than what he had paid for.

5 u - 1000 = 3 u + 440
5 u - 3 u = 440 + 1000
2 u = 1440

1 u = 1440 ÷ 2 = 720

Number of customers who bought just one file
= 1 u - 600
= 720 - 600
= 120

Answer(s): 120