# Question about geometric series

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• June 1st 2010, 01:38 PM
yida
Question about geometric series
I don't quite understand half-life. How to solve this question?
http://www.mathhelpforum.com/math-he...56ygrthbrh.jpg
• June 1st 2010, 02:54 PM
skeeter
Quote:

Originally Posted by yida
I don't quite understand half-life. How to solve this question?
http://www.mathhelpforum.com/math-he...56ygrthbrh.jpg

$y = y_0\left(\frac{1}{2}\right)^{\frac{t}{h}}$

$y$ = amount left at any time $t$ in hrs

$y_0$ = amount at $t = 0$

$h$ = half-life in hrs
• June 1st 2010, 03:27 PM
yida
the answer is wrong
• June 1st 2010, 04:54 PM
skeeter
Quote:

Originally Posted by yida
the answer is wrong

what answer are you speaking of ?

I gave you the general function for half-life, not an "answer".
• June 1st 2010, 04:58 PM
yida
I use y0=55
t=12 h=7.2
but I got wrong answer
• June 1st 2010, 05:01 PM
skeeter
what "wrong answer" did you get?
• June 1st 2010, 05:04 PM
yida
55(0.5)^(12/7.2)
• June 1st 2010, 05:07 PM
skeeter
Quote:

Originally Posted by yida
55(0.5)^(12/7.2) = 17.324 mg

... and that is not wrong.