Billy bought 3 textbooks. The original price of each textbook was $15. He was given 5% discount on the first textbook and 20% discount on the rest of the textbooks. How much did he pay for the 3 textbooks altogether?
Cost of the first textbook after 5% discount in percent
= 100% - 5%
= 95%

Cost of the first textbook after discount
= 95% x 15
= ⁹⁵₁₀₀ x 15
= $14.25

Number of the rest of the textbooks that enjoyed 20% discount
= 3 - 1
= 2

Cost of each of the rest of the 2 textbooks after 20% discount in percent
= 100% - 20%
= 80%

Cost of each of the rest of the 2 textbooks
= 80% x 15
= ⁸⁰₁₀₀ x 15
= $12

Cost of the rest of the 2 textbooks that enjoyed 20% discount
= 2 x 12 
= $24

Total cost for the 3 textbooks
= 14.25 + 24
= $38.25

Answer(s): $38.25