Goal Seek is a great tool for finding out how much you
need to change a single input value to generate a desired result from a
formula, but it’s of no help if you want to find the best mix of several
input values. For example, marketing vice president Craig Dewar might
want to advertise in four national magazines to drive customers to
Consolidated Messenger’s Web site, but he might not know the best mix of
ads to reach the greatest number of readers. He asked the publishers for
ad pricing and readership numbers, which he recorded in a spreadsheet,
along with the minimum number of ads per publication (three) and the
minimum number of times he wants the ad to be seen (10,000,000). Because
one of the magazines has a high percentage of corporate executive
readers, Craig does want to take out at least four ads in that
publication, despite its relatively low readership. The goal of the ad
campaign is for the ads to be seen as many times as possible without
costing the company more than the $3,000,000 budget.
Tip
It helps to spell out every aspect of your problem so that you
can identify the cells you want Solver to use in its
calculations.
If you performed a complete installation when you installed Excel
on your computer, you see the Solver button on the Data tab in the
Analysis group. If not, you need to install the Solver Add-In. To do so,
click the File tab, and then click Options. In the Excel Options dialog
box, click Add-Ins to display the Add-Ins page. At the bottom of the
dialog box, in the Manage list, click Excel Add-Ins, and then click Go
to display the Add-Ins dialog box. Select the Solver Add-in check box
and click OK to install Solver.
Tip
You might be prompted for the Microsoft Office system
installation CD. If so, put the CD in your CD drive, and click
OK.
After the installation is complete, Solver appears on the Data
tab, in the Analysis group. Clicking Solver displays the Solver
Parameters dialog box.
The first step of setting up your Solver problem is to identify
the cell that contains the summary formula you want to establish as your
objective. To identify that cell, click in the Set Objective box, click
the target cell in the worksheet, and then select the option
representing whether you want to minimize the cell’s value, maximize the
cell’s value, or make the cell take on a specific value. Next, you click
in the By Changing Variable Cells box and select the cells Solver should
vary to change the value in the objective cell. Finally, you can create
constraints that will set the limits for the values Solver can use. To
do so, click Add to open the Add Constraint dialog box.
You add constraints to the Solver problem by selecting the
cells to which you want to apply the constraint, selecting the
comparison operation (such as less than or equal to, greater than or
equal to, or must be an integer), and clicking in the Constraint box to
select the cell with the value of the constraint. You could also type a
value in the Constraint box, but referring to a cell makes it possible
for you to change the constraint later without opening Solver.
Tip
After you run Solver, you can use the commands in the Solver
Results dialog box to save the results as changes to your worksheet or
create a scenario based on the changed data.
In this exercise, you’ll use Solver to determine the best mix of
ads given the following constraints:
-
You want to maximize the number of people who see the
ads.
-
You must buy at least 8 ads in 3 magazines and at least 10 in
the fourth.
-
You can’t buy part of an ad (that is, all numbers must be
integers).
-
You can buy no more than 20 ads in any one magazine.
-
You must reach at least 10,000,000 people.
-
Your ad budget is $3,000,000.
Set Up
-
If the Solver button doesn’t appear in the
Analysis group on the Data tab, follow the instructions from
earlier in this section to install it.
-
In the Analysis group on
the Data tab, click Solver.
The Solver Parameters dialog box opens.
-
Click in the Set Objective
box, and then click cell G9.
$G$9 appears in the Set Objective
field.
-
Click Max.
-
Click in the By Changing Variable
Cells field, and select cells E5:E8.
$E$5:$E$8 appears in the By Changing
Variable Cells field.
-
Click Add.
The Add Constraint dialog box opens.
-
Select cells E5:E8.
$E$5:$E$8 appears in the Cell Reference
field.
-
In the operator list, click int. Then click Add.
Excel adds the constraint to the Solver problem, and the Add
Constraint dialog box clears to accept the next constraint.
Note
In Excel 2010, the Ignore Integer Constraints option is
turned on by default. To turn the option off, in the Solver
Parameters dialog box, click Options. On the All Methods page of
the dialog box, uncheck the Ignore Integer Constraints box and
click OK.
-
Click cell F9.
=$F$9 appears in the Cell Reference
field.
-
Click in the Constraint
field, and then click cell G11.
=$G$11 appears in the Constraint
field.
-
Click Add.
Excel adds the constraint to the Solver problem, and the Add
Constraint dialog box clears to accept the next constraint.
-
Click cell G9.
$G$9 appears in the Cell Reference
field.
-
In the operator list, click >=.
-
Click in the Constraint
field, and then click cell G12.
=$G$12 appears in the Constraint
field.
-
Click Add.
Excel adds the constraint to the Solver problem, and the Add
Constraint dialog box clears to accept the next constraint.
-
Select cells E5:E7.
$E$5:$E$7 appears in the Cell Reference
field.
-
In the operator list, click >=.
-
Click in the Constraint
field, and then click cell G13.
=$G$13 appears in the Constraint
field.
-
Click Add.
Excel adds the constraint to the Solver problem, and the Add
Constraint dialog box clears to accept the next constraint.
-
Click cell E8.
$E$8 appears in the Cell Reference
field.
-
In the operator list, click >=.
-
Click in the Constraint
field, and then click cell G14.
=$G$14 appears in the Constraint
field.
-
Click Add.
Excel adds the constraint to the Solver problem, and the Add
Constraint dialog box clears to accept the next constraint.
-
Select cells E5:E8.
$E$5:$E$8 appears in the Cell Reference
field.
-
Verify that the <=
operator appears in the operator field, click in the Constraint field, and then click cell
G15.
=$G$15 appears in the Constraint
field.
-
Click OK.
Excel adds the constraint to the Solver problem and closes the
Add Constraint dialog box, and the Solver Parameters dialog box
opens again.
-
Click Solve.
The Solver Results dialog box opens, indicating that Solver
found a solution. The result is displayed in the body of the
worksheet.
-
Click Cancel.
The Solver Results dialog box closes.
Clean Up
Save the AdBuy workbook, and then close it.
