<PRE><B>Question 1091248</B>
600000*b^t, where t=30=15000
b^30=15000/600000=1/40
30 ln b=ln (1/40)=-3.689
divide by 30 without rounding
ln b=-0.1230.
raise both sides to the e power
b=0.8843
600000*0.8843^t=5
divide by 600000
0.8843^x=5/600000=0.000008333
logs of both sides
x log (0.8843)=-5.079
x=-5.079/log (0.8843)=95.12 years ANSWER
check
in 30 years, it decreases 1/40
in 60 years, 1/1600
in 90 years, 1/64000
so it will decrease somewhat more than 1/64000
600000*(0.8843)^95=5.07</PRE>