You need to look at using solver. Tools=Solver. (it is an addin, so you
might need to install it, but it is included in the Office CD). There is a
sample file shipped with excel that has a problem of this nature in it.

Notationally, A, B and C are usually used to denote the coefficients of the
equation meaning they are the fixed cost or per unit profit or whatever you
are dealing with. x, y and z would be used to denote the percentages or
quantities of each resource which you solve for. So A, B, C would be fixed
for the duration of the problem.

Good luck in school.
--
Regards,
Tom Ogilvy

"Simon" wrote in message
...
I need to solve a business problem which can be expressed as

Ax + By +Cz = T

where I need to find A, B and C

x, y and z are constant (for the duration of the equation) and known
A, B and C are subject to a constraint such that A, B and C must not
exceed a given percentage of (A+B+C)

I need to be able to roll a solution across several columns (representing
months of the year) in a worksheet - any ideas on how to do it?

The business problem behind this is...

1. Need to generate a certain level of income from 3 types (A, B & C) of
resource (call this level Target or T)
2. Resources generate income at a rate of x, y and z per month
3. Must be able to specify the resource mix - eg 60% of total resources
must be A, 25% B and 15% C
4. what (for any given value of T) is the correct resource mix? ie what
are the values of A, B and C

any help greatly valued

thanks

Simon