SOLUTION: How long will it take for an investment to double at 3% a year. Simple interest rate. ( I know this easy and the answer is 20 but I can not figure out how to get it)

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Question 1068716: How long will it take for an investment to double at 3% a year. Simple interest rate. ( I know this easy and the answer is 20 but I can not figure out how to get it)
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Simple interest,
I=Prt
So the future value would be,
F=P%2BI
F=P%2BPrt
F=P%281%2Brt%29
2P=P%281%2Brt%29
1%2Brt=2
rt=1
0.03t=1
t=1%2F0.03
t=33.3yrs
.
.
.
If it's compounded interest,
2P=P%281%2Bi%29%5Et
2=%281.03%29%5Et
t=log%28%282%29%29%2Flog%28%281.03%29%29
t=23.4yrs
.
.
.
Neither equals 20.