Question 994683
P=Po{1+0.04}^n, n=years
2500/2000=(1.04)^n
1.25=(1.04)^n
ln both sides
0.223=nln(1.04)=n(0.3922)
without rounding, divide the 0.223 originally unrounded by 0.3922 unrounded.
The result is 5.69 years.
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Check.
the first year, the interest is $80, and that increases slightly each year.  After 6 years, it would be $480 if the increase weren't factored in, so the answer is reasonable.