Question

At the start of the week a bookshop had science and art books in the ratio 2:5. By the end of the week, 20% of each type of books were sold and 2240 books of both types were unsold. How many books of each type were there at the start of the week?

Answer 1

Let there be 2x science and 5x art books 
science books sold = 2x × 0.2 = 0.4x 
science books unsold = 2x – 0.4x = 1.6x 

art books sold = 5x × 0.2 = x 
art books unsold = 5x – x = 4x 

total books unsold = 1.6x + 4x = 5.6x 
5.6x = 2240 
x = 400 

2x science = 800 
and 5x art books = 2000