If the base of a rectangle is increased by 10% and the area is unchanged, by what percentage is the width decreased by ?
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? ...
Prove that the shaded area of the semicircle is equal to the area of the inner circle.
A useful strategy for working out percentages of quantities is to work out 10% first, and then use fractions or multiples of that amount.