SOLUTION: 1. Arsenic-74 is used to locate brain tumors. It has a half-life of 17.5 days. Write an exponential decay function for a 90-mg sample. Use the function to find the amount remaining

Algebra ->  Logarithm Solvers, Trainers and Word Problems -> SOLUTION: 1. Arsenic-74 is used to locate brain tumors. It has a half-life of 17.5 days. Write an exponential decay function for a 90-mg sample. Use the function to find the amount remaining      Log On


   

Question 136165: 1. Arsenic-74 is used to locate brain tumors. It has a half-life of 17.5 days. Write an exponential decay function for a 90-mg sample. Use the function to find the amount remaining after 6 days?
PLEASE HELP ME. (sorry for caps im not shouting it just I've been having trouble and no has been helping me)-thank you
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
The formula for a half-life function is


A%5Br%5D=A%5B0%5D%281%2F2%29%5E%28t%2FH%29 where A%5Br%5D is the amount remaining, A%5B0%5D is the original amount of the substance, and H is the half-life


So in our case A=90 and H=17.5

A%5Br%5D=90%281%2F2%29%5E%28t%2F17.5%29 Plug in A%5B0%5D=90 and H=17.5

A%5Br%5D=90%281%2F2%29%5E%286%2F17.5%29 Since we want to know how much is remaining after 6 days, simply plug in t=6


A%5Br%5D=90%281%2F2%29%5E%280.34286%29 Divide


A%5Br%5D=90%280.78847%29 Raise 1%2F2 to the 0.34286th power to get 0.78847


A%5Br%5D=70.9623 Multiply


So in 6 days, there will be about 70.9623 mg of arsenic left over