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Question
radioactivity decay:Let q represent a mass of radioactive radium(226^Ra)(in grams ), whose half life is 1620 years.
the quantity of radium present after t years is
Q=25(1/2)^t/1620.
(a)Determine the initial quantity (when t=0)
(b) Determine the quantity present after 100 years
(c) graph the function over the interval t=0 to  t=5000

Answer
There should be parentheses around the exponent:
Q = 25()^(t/1620)

The initial quantity is 25 g.
The quantity after 100 years is approximately 23.95 g:
http://www.flickr.com/photos/dwread/8451347843/

The quantity after 5000 years is approximately 2.94 g
http://www.flickr.com/photos/dwread/8451347809/  

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I can answer questions in Algebra, Basic Math, Calculus, Differential Equations, Geometry, Number Theory, and Word Problems. I would not feel comfortable answering questions in Probability and Statistics or Topology because I have not studied these in depth.

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