PSLE
A stationery shop is having a book sale. The 1st book is at 5% 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. Shiyun's books were priced at $31 and $33. How much more did she pay for the 1st book than the 2nd book? 
2. David paid a total of $47.40 for his two books. He paid $5.80 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% $31
Discount	- 5%	- 20%
Sale price	95%	80%	?

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

Selling price of 2nd book
= 80% x 31
= ⁸⁰₁₀₀ x 31
= $24.80

Amount that Shiyun paid more for the 1st book than the 2nd book
= 31.35 - 24.80
= $6.55

	1st book	2nd book	Total amount
Original price	100%	100%
Discount	- 5%	- 20%
Sale price	95%	80%
Compare 1st book and 2nd book	1 u + $5.80	1 u	$47.40

(b)
Sale price of the 1st book = 1 u + 5.80
Sale price of the 2nd book = 1 u

Total amount that David paid
= 1 u + 5.80 + 1 u
= 2 u + 5.80

2 u + 5.80 = 47.40
2 u = 47.40 - 5.80
2 u = 41.60

1 u = 41.60 ÷ 2 = 20.80

Sale price of the 1st book
= 1 u + 5.80
= $26.60

95% of the price = $26.60
100% of the price = ^26.60₉₅ x 100 = $28

Selling price of the 1st book before discount = $28

Answer(s): (a) $6.55; (b) $28