If the base of a rectangle is increased by 10% and the area is
unchanged, by what percentage (exactly) 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.
Last year, on the television programme Antiques Roadshow, a painting was said to be worth £15,000 although the painting originally cost only 50p. As a percentage of the original price, what would be the approximate profit if the painting were to be sold for £15,000?
If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.
This problem is taken from the UKMT Mathematical Challenges.