Originally Posted by

**astuart** I'm trying to solve the following problem...

Three hundred students attended the dedication ceremony of a new building on a college campus. The president of the traditionally female college announced a new expansion program, which included plans to make the college co-educational. The number of students who learned of the new program 't' hours later is given by the function...

$\displaystyle f(t) = 3000 / (1 + Be^{-kt})$

If 600 students on campus had heard about the new program 2 hours after the ceremony, how many students had heard about the policy after 4 hours?

I've tried to tackle this two ways - by solving for b, and solving for k.

I'm assuming here that $\displaystyle f(0) = 3000 / (1 + Be^{-k[0]}) = 300$ and that $\displaystyle f(2) = 3000 / (1 + Be^{-2k}) = 600$

If f(0) = 300, then 3000 / 10 = 300. Therefore, '1 + B e^-k(0)' has to equal 10. This would mean that B = 9 (as e^0 = 1).

However, if I use 9 as B, when i plug that into the original equation and try and solve f(4), I get the wrong answer - about 2848, when I should be getting 1080.

I then tried to solve f(2) = 600, then solve for B and k.

$\displaystyle f(2) = 3000 / (1 + Be^{-k[2]}) = 600$

I reach an issue where using 9 for B (As in the original equation) doesn't work, and I can't figure out how to isolate one variable without knowing the other..