Primary 6 · Percentage · Question type 3.4

P6 Percentage: Percentage Questions with an Unchanged Quantity

One quantity stays unchanged. Its percentage falls because the total used as 100% increases.

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Primary 6, on the MOE Primary Mathematics syllabus.

In the Percentage chapter9 question types · see the chapter

The lesson · 3 minutes 9 seconds

How do you solve P6 percentage questions with an unchanged quantity?

Watch: 60 basketball cards added, and football falls from 40% to 25%

Another worked example

A worked example

A shop had silver and gold balloons. Silver balloons made up 75% of the balloons. The shop bought some gold balloons, and silver balloons then made up 60% of the balloons. The shop then bought 60 more gold balloons, and silver balloons made up 50% of the balloons. How many silver balloons were there?

The working · Eleven lines

The step-by-step working

Written out in full, the way it should appear on paper.

the silver balloons never changed, only gold balloons were bought
at first, silver = 75% = 75/100 = 3/4 of the balloons
after the first buy, silver = 60% = 60/100 = 3/5 of the balloons
in the end, silver = 50% = 50/100 = 3/6 of the balloons
silver balloons = 3 units at every stage
balloons at first = 4 units
balloons after the first buy = 5 units
balloons in the end = 6 units
the second buy = 6 units - 5 units = 1 unit
1 unit = 60
3 units = 3 × 60 = 180 silver balloons

The answer is 180.

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Find the pens left

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A shop had only red pens and blue pens. Red pens made up 40% of the pens. After 240 red pens were sold, red pens made up 20% of the pens. How many pens were left in the shop?

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the blue pens never changed, only red pens were sold
at first, blue pens = 100% - 40% = 60% = 60/100 = 12/20 of the pens
in the end, blue pens = 100% - 20% = 80% = 80/100 = 12/15 of the pens
blue pens = 12 units in both totals
pens at first = 20 units
pens in the end = 15 units
red pens sold = 20 units - 15 units = 5 units
5 units = 240
1 unit = 240 ÷ 5 = 48
15 units = 15 × 48 = 720 pens

Ans: 720

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