KS3

How to work out percentage increase (decimal method)

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A short video showing how to work out percentage increase.

How to work out percentage increase slideshow

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Click to see a step-by-step slideshow.
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WHAT YOU NEED: whiteboard, marker pen, calculator and ruler.
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STEP 1: Write out the problem and circle the key pieces of information. Draw a bar, labelling the original amount - in this case 16. Shade the bar in. Draw another bar directly underneath. Shade and label it 100%.
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STEP 2: Roughly estimate what the extra 25% would look like and add this area onto the end of the bottom bar. Label this extra area 25% and label 125% at the end of the bar.
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STEP 3: Add the same area onto the end of the top bar and label the whole bar with a question mark. Convert each percentage to a decimal. On the bottom bar change the 100% label to 1, change the 125% label to 1.25 and change the 25% label to 0.25.
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STEP 4: Multiply the original amount by the decimal to find the new amount. Here it's 16 multiplied by 1.25. Before you use a calculator, can you estimate the answer in your head?
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Use a calculator to check your answer.
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You’ve done it! Now you know that when you add 25% to 16 you get 20.

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