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**Piggins** I;m having trouble with some questions on exponential growth. All of them seem to end with the same type of equation, one that I cannot figure out.

They will; end something like this..

2=1.15^x (1.15 to the power of x)

On simpler questions like this, you had to find a common base.

ie. 27=3^x. 3^3=3^x therefore x=3

But I don't see how you can find a common base wth 2 and 1.15, or other such numbers (where one has many decimal places-for example, one question ended up as 9=1.076842^x).

The question that ended with 2=1.15^x was as follows: A bacteria grows at 15% per day. In how many days will it have doubled?

Anybody have any ideas?