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Microsoft: Office FAQ

Best of Excel

Which of these numbers add up to my target number?? by KenWright
Posted: 20 Jan 04 (Edited 9 May 04)

If you are looking for a solution (Not necessarily the only one) to a subset of a group of numbers that will add up to a target number, then this can be done quite simply with Solver.

Assuming range of numbers in A1:A30, add a set of 0s in B1:B30 and in say B31 put

=SUMPRODUCT(A1:A30*B1:B30)

Now do Tools / Solver / Set Target Cell 'B31' to 'value of' and put in your target
number.  Then, using the range selector under the 'By Changing cells' section, select cells B1:B30 as the ones to change and hit enter which will take you back to the first dialog box.  Now hit the 'Add' button, and add the constraint that B1:B30 must be 'bin' (Means binary as in 1 or 0, and it's one of the dropdowns, so just hit the arrow and select 'bin') and just hit Solve.  You MUST ensure that in this example, when you add the 'bin' constraint range, you do not inadvertantly include the formula cell B31, else you will get an error message such as 'Binary Contsraint cell reference must include only adjustable cells'

Won't do any more than single solution, but for a Finance Dept that will often
suffice in this context.

[color green]Thanks to Henio as well for the following link, which will give you a helpful tutorial at http://www.solver.com/stepbystep.htm
and which walks you through an interesting scenario and explains what you can do with the tool.
[/color]

If you are going to look for more than one target number in the data, then with
that formula in say B31, in B32 type the target number, and in B33 put =B32-B31.
Now have Solver solve B33 = to 0 with the same constraints.  Saves having to
change any values in Solver that way, just type what you want in B32.

Looks quite neat too if you format B1:B30 to a white Font and then use
conditional formatting to highlight values in Col A where Val in Col B = 1

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