Ian bought 3 guide books. The original price of each guide book was $36. He was given 10% discount on the first guide book and 25% discount on the rest of the guide books. How much did he pay for the 3 guide books altogether?
Cost of the first guide book after 10% discount in percent
= 100% - 10%
= 90%

Cost of the first guide book after discount
= 90% x 36
= ⁹⁰₁₀₀ x 36
= $32.40

Number of the rest of the guide books that enjoyed 25% discount
= 3 - 1
= 2

Cost of each of the rest of the 2 guide books after 25% discount in percent
= 100% - 25%
= 75%

Cost of each of the rest of the 2 guide books
= 75% x 36
= ⁷⁵₁₀₀ x 36
= $27

Cost of the rest of the 2 guide books that enjoyed 25% discount
= 2 x 27 
= $54

Total cost for the 3 guide books
= 32.40 + 54
= $86.40

Answer(s): $86.40