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Percentage Unchanged

If the base of a rectangle is increased by 10% and the area is unchanged, by what percentage is the width decreased by ?

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Circle Packing

Equal circles can be arranged so that each circle touches four or six others. What percentage of the plane is covered by circles in each packing pattern? ...

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Round and Round

Prove that the shaded area of the semicircle is equal to the area of the inner circle.

Antiques Roadshow

Age 14 to 16 Short Challenge Level:

Answer: 3,000,000%

£15,000 $-$ 50p = £14,999.50 as a % of 50p
£14,999.50 $\approx$ £15,000
     50p   =   100%
      £1    =   200%
  £1000  = 200,000%
£15,000 = 3,000,000%

This problem is taken from the UKMT Mathematical Challenges.
You can find more short problems, arranged by curriculum topic, in our short problems collection.