From time to time you want want to do some basic algebra. Forget about pen and paper ...
Mathomatic's a open source website with a simple online tool.
Here' s what I just used it for: converting annual interest into a monthly compounding equivalent (I wanted the formula for a spreadsheet).
The starting point is this
arate = (1+mrate)^12-1
which says that the annual interest rate is 12 months of compounded monthly interest.
I wanted to rewrite this in terms of the monthly rate.
Using Mathomatic, I execute these two lines:
arate = (1+mrate)^12-1
mrate
and click the "Run Mathomatic" button
Entering "mrate" on its own tells Mathomatic to solve for it.
so it spits out
mrate = (((1 + arate)^––)·sign) ? 1
The "sign" you can ignore: it means you can put plus or minus at that point to get two solutions; just treat it as +1, that is, ignore it.
How easy is that! There are some more tips here