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.
Can you find the pairs that represent the same amount of money?
If the base of a rectangle is increased by 10% and the area is unchanged, by what percentage (exactly) is the width decreased by ?