Question 989720
FV = PV * ( 1 + I ) ^ N 
1) solve for I
divide both sides of = by PV
( 1 + I ) ^ N = FV / PV
take the Nth root of both sides of =
1 + I = ( FV / PV ) ^ (1 / N )
subtract 1 from both sides of = 
I = ( ( FV / PV ) ^ (1 / N ) ) - 1
2) solve for N
divide both sides of = by PV
use definition of logarithm - log base a of X = N means a ^ N = X
N = log base (I + 1) of ( FV / PV )