Siti buys a laptop at Courts Megastore. She receives a 20% discount off the original price. GST of 9% is then applied to the discounted price. Siti pays a total of $1,090. What was the original price of the laptop before the discount?
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Worked Solution
Step 1: Identify the forward multiplier chain.
Discount of 20% → multiply by 0.80
GST of 9% on discounted price → multiply by 1.09
So: original × 0.80 × 1.09 = $1,090
Step 2: Compute the combined multiplier.
0.80 × 1.09 = 0.872
Step 3: Solve for the original price.
Original = $1,090 ÷ 0.872 = $1,250
Verification (working forward):
Discounted price = $1,250 × 0.80 = $1,000
GST amount = $1,000 × 0.09 = $90
Final price = $1,000 + $90 = $1,090 ✓
The original price of the laptop was $1,250.
Correct answer: $1,250
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