KS3

How to work out a percentage of an amount (1% method)

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A short video showing you how to work out a percentage of an amount using the 1% method.

Work out percentages slideshow

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Click to see a step-by-step slideshow.
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WHAT YOU NEED: whiteboard, calculator and 3 marker pens.
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STEP 1: Write the problem and circle the key information. Here it is the total amount, 70 g, and the percentage you want to find, 20%. Draw a bar and label with the total amount which is 70 g. Draw a bar below and label it 100%.
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STEP 2: Estimate where 20% lies and mark it with a vertical line. Shade the area in and label it 20%. Draw a vertical line above this on the top bar and shade it in, labelling it with a question mark...
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...then erase the shaded area on the bottom bar and estimate where 1% lies. Draw a vertical line to show this and label it 1%. Erase the shaded area on the top bar. Draw a vertical line above the 1% line and label it with a question mark.
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STEP 3: Write out the equation to find 1% of the total amount. Here it is 70 g ÷ 100. Before you use a calculator, can you estimate what the answer will be? Now use a calculator to check your answer. You should find this is 0.7 g.
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STEP 4: Write out the equation to find 20% of the total amount. Here it is 20 × 0.7 g. Before using a calculator for your answer, can you estimate it? Now use a calculator to find the answer.
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That’s it! You found 1% of 70 g and multiplied it by 20, giving the answer 14 g.

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