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?

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 

Where is the qeustion