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 ?

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? ...

Round and Round

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

Age 14 to 16 Short Challenge Level:

£15,000 $-$ 50p = £14,999.50 as a % of 50p
£14,999.50 $\approx$ £15,000