Oliver bought 5 colouring books. The original price of each colouring book was $15. He was given 15% discount on the first colouring book and 20% discount on the rest of the colouring books. How much did he pay for the 5 colouring books altogether?
Cost of the first colouring book after 15% discount in percent
= 100% - 15%
= 85%

Cost of the first colouring book after discount
= 85% x 15
= ⁸⁵₁₀₀ x 15
= $12.75

Number of the rest of the colouring books that enjoyed 20% discount
= 5 - 1
= 4

Cost of each of the rest of the 4 colouring books after 20% discount in percent
= 100% - 20%
= 80%

Cost of each of the rest of the 4 colouring books
= 80% x 15
= ⁸⁰₁₀₀ x 15
= $12

Cost of the rest of the 4 colouring books that enjoyed 20% discount
= 4 x 12 
= $48

Total cost for the 5 colouring books
= 12.75 + 48
= $60.75

Answer(s): $60.75