Excel 2007 : Minimum Number Required to Reach Goal

[ikevinax]

I'm sure this is answered somewhere but I don't know the correct terms to use to search effectively.

Given: I am taking tests on which I can receive grades of A, B, or C. I have currently completed 45 tests 64% of which have a grade of A. I don't know how many test I will be given between now and a deadline of end of the semester.

I would like to know how to calculate the number of As I would have to receive in order to end with a percentage of 85% minimum - assuming that I don't receive any more Bs or Cs.

[MrShorty]

Setup the algebra:

% of A's = num of A's/num of tests -- .64=n(A)/45 n(A)=29 currently

x=0.85=(29 + e)/(45 + e) where e is the number of tests to be taken, and assuming you get an A on each. Now solve for e.

This will answer the question of "how many more tests do I need to take, if I get an A on each, to end up with a minimum of 85% A's." There might be more to the question (implied by, "I don't know how many test I will be given...").