PSLE
A store is having a book sale. The 1st book is at 10% discount. The 2nd book is at 20% discount. The price of the 2nd book should be equal or lower than the price of the 1st book.

1. Ivory's books were priced at $28 and $38. How much more did she pay for the 1st book than the 2nd book? 
2. Justin paid a total of $38.70 for his two books. He paid $9.90 less for the 2nd book than for the 1st book. What was the price of the 1st book before discount? 

	1st book	2nd book	Total amount
Original price	100% $38	100% $28
Discount	- 10%	- 20%
Sale price	90%	80%	?

(a)
Selling price of the 1st book
= 90% x 38
= ⁹⁰₁₀₀ x 38
= $34.20

Selling price of 2nd book
= 80% x 28
= ⁸⁰₁₀₀ x 28
= $22.40

Amount that Ivory paid more for the 1st book than the 2nd book
= 34.20 - 22.40
= $11.80

	1st book	2nd book	Total amount
Original price	100%	100%
Discount	- 10%	- 20%
Sale price	90%	80%
Compare 1st book and 2nd book	1 u + $9.90	1 u	$38.70

(b)
Sale price of the 1st book = 1 u + 9.90
Sale price of the 2nd book = 1 u

Total amount that Justin paid
= 1 u + 9.90 + 1 u
= 2 u + 9.90

2 u + 9.90 = 38.70
2 u = 38.70 - 9.90
2 u = 28.80

1 u = 28.80 ÷ 2 = 14.40

Sale price of the 1st book
= 1 u + 9.90
= $24.30

90% of the price = $24.30
100% of the price = ^24.30₉₀ x 100 = $27

Selling price of the 1st book before discount = $27

Answer(s): (a) $11.80; (b) $27