# Math Analysis

posted by
**Emily**
.

31. Radioactive decay of material is determined using the formula N = Noe^-kt. Find the constant k for Plutonium-239 given that its half-life is 24,390 years.

==> I don't really get where to start here because the problem does not give you how much Plutonium-239 there is. I just need a hint, no need to work out the entire problem for me please :)

35. The exponential growth rate of the population of Europe west of Russia is 1% per year. What is the doubling time?

==> I just used the rule of 72 to estimate it out to be about 72 years, but I don't think this is the correct process. Can anyone help me on these? Thanks so much!! :)