SOLUTION: Josh wants to double his $20,000 in 6 years. What interest rate does Josh need?

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Question 1111059: Josh wants to double his $20,000 in 6 years. What interest rate does Josh need?
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
Rule of 72 would say 72/6=12% interest
40000=20000(1+r)^6
2=(1+r)^6
ln 2=6 ln (1+r)
0.693=6 ln(1+r)
0.693/6=0.1155=ln(1+r)
raise everything to e power
1.122=1+r
r=0.122 or 12.2% interest