Answer
After 12 years Emily's salary will be doubled
Explanation
Here the salary increase can be considered as increase in the principle amount annually.
There are two methods to calculate the number of years.
1) 72 Rule
The rule state that, the number of years required to double the principle amount at given rate of interest, we just divide 72 by the interest rate.
In this problem Principle amount =$25,000 (in this rule no importance in principle amount)
Rate of interest, R = 6%
Number of years taken to double the amount = 72/6 =12 years
2)compound interest calculation method
P[1+R/100]^N = 2P
[1+ R/100 ]^N= 2
R is 6%, N is number of years
(1.06)^N =2
e^(ln(1.06^N)) = 2
e^N㏒(1.06)=2
N x ㏑(1.06) = ㏑(2)
N =㏑(2)/㏑(1.06) ≈11.8917 ≈ 12 years
