课爱 classai 中文

Topics › Percentage › Q111

Percentage · increase then decrease

P6 · Percentage · PSLE Maths

Question

At a shop in Toa Payoh, the price of a pair of sports shoes was first increased by 20%. Later, during a sale, the new price was decreased by 25%. The sale price was $72. What was the original price of the shoes?

Try it yourself · watch the animation →

Hint

Take the original price as 100% and draw 10 units. How many units after the 20% increase? The 25% decrease is 25% of the new price.

Show the answer and step-by-step explanation

Answer: Original price 80 $

  1. Original is 100% — First, take the original price as 100%. Split 100% into 10 equal units, so each unit is 10%.
  2. Increase by 20% — An increase of 20% means adding 2 units. So the new price is 120%, or 12 units in all.
  3. Decrease by 25% — Be careful: the 25% decrease is taken from the increased price. There are 12 units after the increase. 25% is one quarter, and 1/4 of 12 units is 3 units.
  4. 9 units left — After the sale, 12 − 3 = 9 units are left. The question says these 9 units are $72.
  5. Find original — 9 units = $72, so 1 unit = $72 ÷ 9 = $8. The original price is 10 units: 10 × $8 = $80. 📌 Key idea: in successive percentage changes, the later percentage is based on the changed amount, not always the original 100%.

Method: Use a 100% bar model for the original amount. Extend the bar for the percentage increase, then reduce the required percentage from the increased bar. Match the remaining units to the final amount given.

Practice: 3 similar questions

  1. The price of a T-shirt was first increased by 20% and later decreased by 10%. Its final selling price was $54. What was its original price?
    Answer

    50 $ — The original price is 100%. After a 20% increase, it becomes 120%. After a 10% decrease, 90% × 120% = 108% of the original price remains. 108% corresponds to $54, so 1% corresponds to $0.50 and 100% corresponds to $50.

  2. Raju's number of cards first increased by 30%. Later, he gave away 20% of the cards he then had and had 208 cards left. How many cards did Raju have at first?
    Answer

    200 张 — The original number of cards is 100%. After a 30% increase, it becomes 130%. After giving away 20%, 80% × 130% = 104% of the original number remains. 104% corresponds to 208 cards, so 1% corresponds to 2 cards and 100% corresponds to 200 cards.

  3. The price of a bicycle was first increased by 25%. Later, during a sale, it was decreased by 24%. The sale price was $760. What was the original price of the bicycle?
    Answer

    800 $ — The original price is 100%. After a 25% increase, it becomes 125%. After a 24% decrease, 76% × 125% = 95% of the original price remains. 95% corresponds to $760, so 1% corresponds to $8 and 100% corresponds to $800.

Learn it on classai

An animation walks through each step, then 3 similar questions check it stuck; mistakes come back for review after 1, 3 and 7 days.

Open this question →

More Percentage questions