# Math Help - Logirithms-- Need Help!

1. ## Logirithms-- Need Help!

Hi there I have a couple questions I could not solve, if some one could help that would be great

1) Find the half-life if 2000g of mathusiasm decays to 1400g in 80 weeks. Round your answer to nearest week.
-- The formula i get is this 12log(0.7)/log(1/2)=K and my answer is wrong.

2)
Find the half-life if 1000g of tspadium decays to 700g in 3 months. Round your answer to the nearest week.

3)
The half-life of luvinmathism is 8 days. Write the half life equation that shows the percent, P of luvinmathism in math 12 students after t days.

2. ## Re: Logirithms-- Need Help!

Hey Gurp925.

If you have a model y(t) = A*e^(kt) where A = 2000g solve for k where 1400 = 2000*e^(80*k) meaning k = [ln(7/10)]/80 which using R gives:

> log(7/10)/80
[1] -0.004458437

Try using the above hint to solve the others.