How long will it take for the prices in the economy to double at a 9% inflation rate

How long will it take for the prices in the economy to double at a 9% inflation rate? (Round to the nearest year)

Basically, you want to find "n" that answers the equation

2 = 1.09 ^n

This is the formula for compound interest.

That is solved using the logarithms:

log (2) = n * log (1.09)

n = log (2) / log (1.09)

n = 8.04323, so rounding to the nearest year is 8.

Easy you want to know (1.09)^x = 2.00

So you have to use logarithms. log (1.09) * x = log (2.00), x = log(2.00)/log(1.09) = 8.04

So approximately 8 years.

using a simple calculation it is around 8. I just used the rule of 72.