From the information we have, we know that each book costs 1.20 dollars. So we shall say this price is at 100% .
Now we need to form an equation to get the percentage when the books are sold at 0.80 dollars.
100% = 1.20
x = 0. 80
Where x is the new percentage when the sale is at 0.80 dollars.
We cross multiply the equation:
1.20 *x = 0.80 * 100
1.2x = 80
x = 80/1.2
x = 66.7%
Round off 66.7 to the nearest tenth we get 67%
The notebooks are sold at 67% (of the original cost).