If prices increase at a monthly rate of 2.3%, by what percentage do they increase in a year?

In this question, the prices are Increased at a monthly rate of 2.3%. Since you are asked how much the percentage in a year and there is 12 month in a year, then you need to do the calculation 12 times.

The calculation would be (100%+2.3%)^12= 131.37344984%

That would be about 31.37% a year.