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 ?

CD Heaven

All CD Heaven stores were given the same number of a popular CD to sell for £24. In their two week sale each store reduces the price of the CD by 25% ... How many CDs did the store sell at each price?

A Change in Code

There are two sets of numbers. The second is the result of the first after an increase by a constant percentage. How can you find that percentage if one set of numbers is in code?

This problem was designed to explore equivalence of change (ie. if a $10\%$ decrease isn't the opposite of a $10\%$ increase, what is? ) and to move students towards the important Stage 5 concept: exponential growth and decay.