Fabian bought 4 colouring books. The original price of each colouring book was $45. He was given 10% discount on the first colouring book and 20% discount on the rest of the colouring books. How much did he pay for the 4 colouring books altogether?
Cost of the first colouring book after 10% discount in percent
= 100% - 10%
= 90%

Cost of the first colouring book after discount
= 90% x 45
= ⁹⁰₁₀₀ x 45
= $40.50

Number of the rest of the colouring books that enjoyed 20% discount
= 4 - 1
= 3

Cost of each of the rest of the 3 colouring books after 20% discount in percent
= 100% - 20%
= 80%

Cost of each of the rest of the 3 colouring books
= 80% x 45
= ⁸⁰₁₀₀ x 45
= $36

Cost of the rest of the 3 colouring books that enjoyed 20% discount
= 3 x 36 
= $108

Total cost for the 4 colouring books
= 40.50 + 108
= $148.50

Answer(s): $148.50