# Thread: how to solve simple half life? ( gr9 mathematics)?

1. YahooHoo
Join Date
Aug 2007
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1

## how to solve simple half life? ( gr9 mathematics)?

Hey there,

Im studying for math exams (gr9) and I have a half-life question that wasnt taught to me. I did some reading on it and this is what i have so far

Amount left=Amount original(1/2) * time/time half life.

This is my problem : In 30h, a sample solution of plutonium-243 decays to 1/64 of its original amount. Determine the half life of each isottope.

PS:and how would i simply finf the Amount left with all the given required values.

2. YahooHoo
Join Date
Aug 2007
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1
After one half life, you have 1/2 left.
After two half lives, you have 1/4 left.
After three half lives, you have 1/8 left.
After four half lives, you have 1/16 left. (etc. etc.)

Your problem has only 1/64 left. 1/64 is 1/2 to the sixth power. (.5*.5*.5*.5*.5*.5). That means that six half lives have passed.

Since it took 30 hours for six half lives to pass, each half life is (30/6) five hours long.

3. YahooHoo
Join Date
Aug 2007
Posts
2
m(t)=m(0)(1/2)^t/T, T half life.
m(t)///////////M(0)=1/64, t=30hours
1/64=(1/2)^30/T
(1/2)^6=(1/2)^30/T
30/T=6, T=5 hours.