Multiply by 11.
Keep the outside digits. Add them in the middle. Then discover what happens when you need to carry.
Try the examplePercentage swap
If 8% of 50 feels awkward, try 50% of 8. Swap the numbers, keep the answer, and see why it works.
Your numbers
The example is loaded. Try a different number whenever you’re ready.
Make your prediction.
Make a prediction before you reveal the answer. Use the method you just explored.
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Challenge 1 of 5
Why does it work?
A percent means “divide by 100”. So a% of b = (a × b) ÷ 100. Swapping a and b gives (b × a) ÷ 100, the same product. This identity also works above 100%; it does not mean that a percentage increase and a discount are interchangeable.
Where this experiment applies
Try non-negative numbers up to 1,000, with at most two decimal places in each input. This experiment calculates a percentage of a number, not a percentage change.
THE RULE, IN ONE LINE
a% of b = b% of a
The explanation and the answer use the same numbers.One more “aha”?
Two discounts. One surprise.
20% off, then another 20%, gives 36% off overall. Change the offers and watch what happens to the price.
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