Jeremy bought some notebooks at $5 each. He later sold them to his customers at $7 each. For customers who bought three notebooks were given another notebook for free. The customers bought either one or three notebooks. Jeremy gave away 110 free notebooks and collected a total of $730 more than what he had paid for. How many customers bought just one notebook each?

	Notebooks sold	Notebooks given to customers who got 1 notebook each	Notebooks given to customers who got 4 notebooks each
Number	1 u	1 u - 440	440
Value	$5	$7	$7
Total Value	5 u	7 u - $3080	$2310

Since 110 notebooks were given free, there were 110 customers who bought three notebooks each.

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

Total number of notebooks for customers who each bought three notebooks 
= 4 x 110
= 440

Number of notebooks for customers who each bought 1 notebook = 1 u - 440

Total amount collected from customers who bought 1 notebook each
= 7 x (1 u - 440)
= 7 u - 3080

Total amount collected from customers who bought three notebooks each
= 110 x 3 x 7
= $2310

Total amount collected from all the customers
= 7 u - 3080 + 2310
= 7 u - 770

Jeremy collected a total of $730 more than what he had paid for.

7 u - 770 = 5 u + 730
7 u - 5 u = 730 + 770
2 u = 1500

1 u = 1500 ÷ 2 = 750

Number of customers who bought just one notebook
= 1 u - 440
= 750 - 440
= 310

Answer(s): 310