Divide 20% by 100 to obtain its decimal form. Dividing 20% by 100 equals 0.2. Set up an equation as 0.2x = 8 which means 20% of x equals 8. Solve the equation by dividing each side by 0.2, Dividing 0.2 from each side results in x=40 Eight is 20% of 40
So there were 40 books in the room and he took 8 making the books 20% less.
