Denise Sakai Troxell (2000) Solving Equations with Goal Seek for Microsoft Excel 2000.

Denise Sakai Troxell (2000)

Solving Equations

with Goal Seek

for Microsoft Excel 2000


A Simple Problemgrades, grades, grades*…

You would love to have a quiz average of 80 points (or better) in the QTM1300 course by the end of the semester.

Your quiz scores on the first nine quizzes are given in the table below.

Quiz 1 2 3 4 5 6 7 8 9

Score 90 88 78 68 84 82 66 74 72

What score do you need to earn on the 10th and final quiz in order to meet your goal average of 80 points?

* from FCL Excel Notes by Joyce Gordon, Babson College, 1998.


You are looking for

x = score on 10th quiz

so that

Formulate the Problemobtain equation to be solved

90 + 88 + 78 + 68 + 84 + 82 + 66 + 74 + 72 + x = 80

10

Quiz AverageQuiz Average

NOTE: Only use Goal Seek if the equation contains only one variable; has the right-hand side equal to a constant.


Preparing the Worksheet for Goal Seekstart with a blank sheet


Preparing the Worksheet for Goal Seekenter labels and constants

Enter labels in cells A1:A13 and

B1

Enter labels in cells A1:A13 and

B1



NOTE: These labels are not essential for the use of Goal

Seek

NOTE: These labels are not essential for the use of Goal

Seek



Enter constants in cells B2:B10

Enter constants in cells B2:B10

Remember…

74

8

7266828468788890Score

97654321Quiz


Preparing the Worksheet for Goal Seekenter formula

Variable values in cell B11

Variable values in cell B11

Left-hand side of equation in cell B13

Left-hand side of equation in cell B13

NOTE: These cells will be colored to indicate that they are essential for Goal

Seek

NOTE: These cells will be colored to indicate that they are essential for Goal

Seek

x

Remember…

90 + 88 + 78 + 68 + 84 + 82 + 66 + 74 + 72 + x = 80

10



Click on cell B13Click on cell B13

Remember…

90 + 88 + 78 + 68 + 84 + 82 + 66 + 74 + 72 + x = 80

10



Type in =AVERAGE(Type in =AVERAGE(

Remember…

90 + 88 + 78 + 68 + 84 + 82 + 66 + 74 + 72 + x = 80

10



Remember…

90 + 88 + 78 + 68 + 84 + 82 + 66 + 74 + 72 + x = 80

10

Highlight cells B2:B11

Highlight cells B2:B11



Type in ) and hit Enter

Type in ) and hit Enter

Remember…

90 + 88 + 78 + 68 + 84 + 82 + 66 + 74 + 72 + x = 80

10



NOTE: Alternative formula for cell B13: =(B2+ B3+ B4+ B5+ B6+ B7+ B8+ B9+ B10+ B11)/10NOTE: Alternative formula for cell B13: =(B2+ B3+ B4+ B5+ B6+ B7+ B8+ B9+ B10+ B11)/10



NOTE: The function AVERAGE entered in cell B13 returns the average of the values in cells B2:B11;

blank cells are ignored

NOTE: The function AVERAGE entered in cell B13 returns the average of the values in cells B2:B11;

blank cells are ignored


Using Goal Seekinvoke Goal Seek

Click on ToolsClick on Tools



Click on Goal Seek

Click on Goal Seek


Using Goal Seekcomplete the Goal Seek dialog box


NOTE: The cell displayed in the Set cell: box must contain the formula for the left-hand side of the

equation (cell B13)

NOTE: The cell displayed in the Set cell: box must contain the formula for the left-hand side of the

equation (cell B13)



Click on the To value:

box

Click on the To value:

box



Type in 80Type in 80

NOTE: The value displayed in the To value: box must be the constant on the right-hand side of the

equation (80)

NOTE: The value displayed in the To value: box must be the constant on the right-hand side of the

equation (80)



Click on the By changing

cell: box

Click on the By changing

cell: box




NOTE: The cell displayed in the By changing cell: box must be the cell containing variable values

(cell B11)

NOTE: The cell displayed in the By changing cell: box must be the cell containing variable values

(cell B11)


Using Goal Seekexecute Goal Seek

Click on OKClick on OK


Using Goal Seekread solution

You need to earn a score of 98 on the 10th quiz to meet

your goal average of 80 points.

You need to earn a score of 98 on the 10th quiz to meet

your goal average of 80 points.

NOTE: If the equation has multiple solutions, Goal Seek usually finds the closest solution to the initial

variable value.

NOTE: If the equation has multiple solutions, Goal Seek usually finds the closest solution to the initial

variable value.


Using Goal Seekend execution

Click on OK

Click on OK

Back to studying!


Final CommentsGoal Seek might not find the exact solution…

Goal Seek has a precision of 0.001:

when the variable value returned by Goal Seek is

plugged into the left-hand side of the equation, the

result will be within 0.001 of the right-hand side;

use Excel Solver for higher precision and/or

equations with multiple variables.

Denise Sakai Troxell (2000) Solving Equations with Goal Seek for Microsoft Excel 2000.

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