Seth bought 3 guide books. The original price of each guide book was $10. He was given 25% discount on the first guide book and 30% 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 25% discount in percent
= 100% - 25%
= 75%

Cost of the first guide book after discount
= 75% x 10
= ⁷⁵₁₀₀ x 10
= $7.50

Number of the rest of the guide books that enjoyed 30% discount
= 3 - 1
= 2

Cost of each of the rest of the 2 guide books after 30% discount in percent
= 100% - 30%
= 70%

Cost of each of the rest of the 2 guide books
= 70% x 10
= ⁷⁰₁₀₀ x 10
= $7

Cost of the rest of the 2 guide books that enjoyed 30% discount
= 2 x 7 
= $14

Total cost for the 3 guide books
= 7.50 + 14
= $21.50

Answer(s): $21.50