Please help with fraction breakdown

Question

A bookshop owner adds three tenths to the price of each book he sells to a customer. If a new book costs the customer $15.60, how much did it cost the bookshop owner?

Answer 1

Let C = cost to owner

C

3/10 C + C = purchase price = $15.60

adding 3/10 C + C give you 1 3/10 C which is = 13/10 C

13/10 C = $15.60 and dividing both side by 13/10 or multiplying both sides by 10/13 you get...

C = $12 which is the cost of the book to the dealer.

 

Check:

$12 x 3/10 = $3.60

Add $3.60 to $12 = $15.60 √