# Math - Algebra

posted by Mitchel

Need help understanding this problem. Looks like an exponential growth/decay.

Magnesium-27 has a half life of 9.45 minutes and can be described by using the equation “y=ae^-kt .

What is the decay constant (k) for Magnesium-27?

How many mg of Magnesium-27 will remain after 1.5 hours from an initial amount of 1000 mg?

How long will it take for 1000 mg of Magnesium to decrease to 780 mg?

Any explanation would be greatly appreciated!!

1. Steve

the amount halves every 9.45 minutes, so

y = a(1/2)^(t/9.45)
but,1/2 = e^-0.693 so

y = a(e^-0.693)^(t/9.45) = ae^(-0.0733t)
where t is in minutes

Now use that to evaluate your other questions

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