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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 ?

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? ...

Fractions and Percentages Card Game

Can you find the pairs that represent the same amount of money?

Round and Round

Age 14 to 16
Challenge Level

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

Circle inside semicircle

What percentage of the sector OAB is taken up with the inner circle?

Circle inside quarter circle

What happens if angle AOB is less than 90 ° or between 90 and 180 degrees?