Thor invests some money in an account earning 8% interest, compounded continuously. After how many years will he double his investment? [Use the formla A = Pert and round answer to the nearest tenth.]
A) 6.2 years
B) 7.5 years
C) 8.7 years
D) 9.9 years

Question

Thor invests some money in an account earning 8% interest, compounded continuously. After how many years will he double his investment? [Use the formla A = Pert and round answer to the nearest tenth.]
A)	6.2 years	
B)	7.5 years	
C)	8.7 years	
D)	9.9 years

jim_thompson5910 · Answer

A = P*e^(rt)
2P = P*e^(rt) ... replace A with 2P (investment P doubling)
2 = e^(r*t)
2 = e^(0.08*t) ... plug in the interest rate r = 8% = 0.08

use natural logs to isolate t