Fred is selling 1200 story books. He sold 75% of them at $10 each, 30% of the remainder at a discount of 20% and the rest at cost price. He made a profit of $2492. Find the cost price of a story book.

Price	$10	$8	Cost Price
Percent	75%	25%
		7.5%	17.5%
Number	900	90	Not needed
Amount collected	$9000	$720	Not needed

Number of story books sold at $10
= 75% x 1200
= ⁷⁵₁₀₀ x 1200
= 900

Price after 20% discount
= 80% x 10
= ⁸⁰₁₀₀ x 10
= $8

Remaining story books
= 1200 - 900
= 300

Number of story books sold at $8
= 30% x 300
= ³⁰₁₀₀ x 300
= 90

Number of story books sold at $10 or 20% discount
= 900 + 90
= 990

Total amount collected from the sale of 900 story books
= 900 x 10
= $9000

Total amount collected from the sale of the other 90 story books
= 90 x 8
= $720

Total amount collected from the sale of story books sold at $10 or 20% discount
= 9000 + 720
= $9720

Cost price of 990 story books
= 9720 - 2492
= $8910

Cost price of 1 story book
= 8910 ÷ 990
= $9

Answer(s): $9