Hello jsu03 Originally Posted by
jsu03 Can someone help me solve for t. Thanks!
(.5)^-(t)/(4.5*10^9) * 100 = 80
I take it that the equation is:$\displaystyle \frac{(0.5)^{-t}}{4.5\times10^9}\times100=80$
So divide both sides by $\displaystyle 100$:$\displaystyle \frac{(0.5)^{-t}}{4.5\times10^9}=0.8$
$\displaystyle \Rightarrow (0.5)^{-t}=0.8\times4.5\times10^9$$\displaystyle =3.6\times10^9$
Take logs (to base $\displaystyle 10$) of both sides:$\displaystyle -t\log(0.5) =\log(3.6)+9$
$\displaystyle \Rightarrow 0.3010t = 9.5563$
$\displaystyle \Rightarrow t = 31.75$
Grandad