## openstudyhelpplease Group Title A certain radioactive element decays according to N=No e ^-kt. If 50% of the original element sample remains after 9 days, what is the decay rate? 10 months ago 10 months ago

1. satellite73 Group Title

you know if $$t=9$$ you have half of what you started with set $e^{9k}=.5$ and solve for $$k$$

2. satellite73 Group Title

you got this? solve in two steps only

how do you solve for k?

4. satellite73 Group Title

1) write in equivalent logarithmic form (take the log) 2) divide by 9

5. satellite73 Group Title

$e^{9k}=.5\iff 9k=\ln(.5)\iff k=\frac{\ln(.5)}{9}$

6. satellite73 Group Title

then if you want a decimal, use a calculator

i have no idea what that means haha. so is it: k= .1831?

8. satellite73 Group Title

no

wait is ln the button on the calculator for e?

10. satellite73 Group Title

http://www.wolframalpha.com/input/?i=ln%28.5%29%2F9 usually $$ln$$ is the button and $$e$$ requires the shift key

ok, so i have to use the shift key right? i tried doing e ^.5 which was 1.64 and then divide that by 9 which was .1831