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## Question

primary 5 | Maths
| Whole Numbers

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At first, blue pen = 5 units

Red pen = 1 unit

Total = 6 units

After, red pen = 2 units

blue pen = 1 unit

Total = 3 units

Since total number of pens is the same, we make the number of units the same.

3 units x 2 = 6 units

So in the end,

Blue pen = 1 units x 2 = 2 units

Red pen = 2 unit x 2 = 4 units

So you can see that number of blue pens decreased by 3 units. Number of red pens increased by 3 units

3 units = 21 pens

1 unit = 21 pens ÷ 3 = 7 pens

Number of red pens in the box at first = 1 unit = 7

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