Question

Dear sir, madam,

I am having a little problem with the solution my chemistry book gives on the following problem:

We have a person whose body vitamine C concentration decays according to the following formula: 1500*0,974^t.

Question A is no problem, but then question B: "Calculate for the intervals 0-30, 30-60, 60-90 the average decay speed of the vitamine C." This is of course a very easy question, but my book seems to forget some values. I should include both boundaries of the interval, right?

Then Question E: "How many mg Vitamine C should the person take in order to keep his body concentration at 1000 mg?" My chemistry book says: take 2.7% of 1000, because that's the average vitamine C loss. However in my opinion, the concentration you need to take after t days to get back to a 1000 mg is described by the formula |1000-1500*0,974^t|. So after 16 days (first time the concentration goes below 1000) you need to take 15.9 mg. What do you think?

Yours sincerely,
Tom Koolen

Answer 1

I think you should go with the book answer. You can calculate decay at 30 and 60 (you provided no units), then take the average of the two. I think that's the single answer provided by the book.