PSLE
A book shop is having a book sale. The 1st book is at 5% discount. The 2nd book is at 10% discount. The price of the 2nd book should be equal or lower than the price of the 1st book.

1. Wendy's books were priced at $4 and $15. How much did she pay for them?
2. Luke paid a total of $39.90 for his two books. He paid $5.70 more for the 1st book than the 2nd book. What was the price of the 2nd book before discount? 

	1st book	2nd book	Total amount
Original price	100% $15	100% $4
Discount	- 5%	- 10%
Sale price	95%	90%	?

(a)
Selling price of the 1st book
= 95% x 15
= ⁹⁵₁₀₀ x 15
= $14.25

Selling price of 2nd book
= 90% x 4
= ⁹⁰₁₀₀ x 4
= $3.60

Total amount that Wendy paid
= 14.25 + 3.60
= $17.85

	1st book	2nd book	Total amount
Original price	100%	100%
Discount	- 5%	- 10%
Sale price	95%	90%
Compare 1st book and 2nd book	1 u + $5.70	1 u	$39.90

(b)
Sale price of the 1st book = 1 u + 5.70
Sale price of the 2nd book = 1 u

Total amount that Luke paid
= 1 u + 5.70 + 1 u
= 2 u + 5.70

2 u + 5.70 = 39.90
2 u = 39.90 - 5.70
2 u = 34.20

1 u = 34.20 ÷ 2 = 17.10

Sale price of the 2nd book = $17.10

90% of the price = $17.10
100% of the price = ^17.10₉₀ x 100 = $19

Selling price of the 2nd book before discount = $19

Answer(s): (a) $17.85; (b) $19