PSLE
A shop is having a book sale. The 1st book is at 5% discount. The 2nd book is at 15% discount. The price of the 2nd book should be equal or lower than the price of the 1st book.

1. Xuan's books were priced at $18 and $33. How much more did she pay for the 1st book than the 2nd book? 
2. Billy paid a total of $36.10 for his two books. He paid $3.80 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% $33	100% $18
Discount	- 5%	- 15%
Sale price	95%	85%	?

(a)
Selling price of the 1st book
= 95% x 33
= ⁹⁵₁₀₀ x 33
= $31.35

Selling price of 2nd book
= 85% x 18
= ⁸⁵₁₀₀ x 18
= $15.30

Amount that Xuan paid more for the 1st book than the 2nd book
= 31.35 - 15.30
= $16.05

	1st book	2nd book	Total amount
Original price	100%	100%
Discount	- 5%	- 15%
Sale price	95%	85%
Compare 1st book and 2nd book	1 u + $3.80	1 u	$36.10

(b)
Sale price of the 1st book = 1 u + 3.80
Sale price of the 2nd book = 1 u

Total amount that Billy paid
= 1 u + 3.80 + 1 u
= 2 u + 3.80

2 u + 3.80 = 36.10
2 u = 36.10 - 3.80
2 u = 32.30

1 u = 32.30 ÷ 2 = 16.15

Sale price of the 1st book
= 1 u + 3.80
= $19.95

95% of the price = $19.95
100% of the price = ^19.95₉₅ x 100 = $21

Selling price of the 1st book before discount = $21

Answer(s): (a) $16.05; (b) $21