2004 AMC 12A Problems/Problem 9
A company sells peanut butter in cylindrical jars. Marketing research suggests that using wider jars will increase sales. If the diameter of the jars is increased by without altering the volume, by what percent must the height be decreased?
When the diameter is increased by , is is increased by , so the area of the base is increased by .
To keep the volume the same, the height must be of the original height, which is a reduction .