You may also like

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.

A Change in Code

Age 14 to 16 Challenge Level:

All numbers in the first column have been increased by the same percentage to give the results shown in the second column.

But the result numbers are disguised - their digits are replaced by letters.

A given letter stands for the same numeral every time it appears in that column.

For example, whatever the C stands for, it stands for that numeral every time the C appears.

Can you work out the percentage change, even with the result digits in code?

a change in code (first)

What about this next set?

It's a new coding - the letters now stand for different numerals.

What is the percentage change used on all numbers in the first column this time?

And here?

Different coding again, and much harder.

By now the problem has definitely become a three star challenge - fancy having a crack at it?