so you want:
7000(1.07^t) = 1400
1.07^t = 2
take log of both sides, and by the rules of logs
t log 1.07 = log 2
t = log2/log1.07 = appr 10.245 years
Use the Rule of 70 to estimate how long it takes a dollar-sign 7000 investment to double if it grows at the annual rate 7 %. Compare with the actual doubling times.
Round your answers to three decimal places.
I found the estimated doubling time using Rule of 70 to be 10.
I am having an issue with finding the actual doubling time in years.
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