A furniture store was having Mother's Day discount of 10% off its usual price. The GST is at 7%. Barbara used her credit card to purchase a sofa bed and Paul used cash to pay for a similar sofa bed.

1. How much did Barbara pay in the end after GST? Round off your answer to the nearest cent.
2. How much did Paul pay in the end after GST? Round off your answer to the nearest ten cent.

New sofa bed Usual Price: $400

Further Discount: Pay by credit card: 10% off discounted price before GST! Pay by cash: $100 off discounted price before GST!

	Credit Card	Cash
Usual Price	$400	$400
Less 10% discount	- $40.00	- $40.00
Price after 10% discount	$360.00	$360.00
Less further discount	- $36.00	- $100
Price after further discount	$324.00	$260.00
Price after GST of 7%	$346.68	$278.20

(a)
New selling price after 10% discount
= 100% - 10%
= 90%

Price of the sofa bed after Mother's Day discount
= 90% x 400
= ⁹⁰₁₀₀ x 400
= $360.00

New selling price after 10% further discount
= 100% - 10%
= 90%

Price of the sofa bed after credit card discount
= 90% x 360.00
= ⁹⁰₁₀₀ x 360.00
= $324.00

Price to pay after including GST
= 100% + 7%
= 107%

Price of the sofa bed after GST
= 107% x 324.00 
= ¹⁰⁷₁₀₀ x 324.00 
≈ $346.68 (Round off to nearest cent)

(b)
Price of the sofa bed after cash discount
= 360.00 - 100
= $260.00

Price of the sofa bed after GST
= 107% x 260.00 
= ¹⁰⁷₁₀₀ x 260.00 
≈ $278.20 (Round off to nearest ten cent)

Answer(s): (a) $346.68; (b) $278.20