Suppose that the Retail Price Index is equal to 87 for 2015. If the base index (2012) had a value of 100, which of the following is likely to be true?

An average, prices fell by 13 per cent since 2012.

All prices rose by 87 per cent since 2012.

On average, prices rose by 13 per cent since 2012.

All prices fell by 13 per cent since 2012.