goal seek equations

8/6/2019 Goal Seek Equations

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Denise Sakai Troxell (2000)

Solving Equations

with Goal Seek

for Microsoft Excel 2000


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A Simple Problem

grades, 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 quizzesare 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.


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You are looking for

x = score on 10th quiz

so that

Formulate the Problem

obtain equation to be solved

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

10

Quiz Average

Quiz Average

NOTE: Only use Goal Seek if the equation

contains only one variable;

has the right-hand side equal to a constant.


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Preparing the Worksheet for Goal Seek

start with a blank sheet


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enter labels and constants

Enter labels in cellsA1:A13 andB1

Enter labels in cellsA1:A13 andB1


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NOTE: These labels are notessential for the use of Goal Seek


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Enter constants incells B2:B10

Enter constants incells B2:B10

Remember

74

8

7266828468788890Score

97654321Quiz


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enter formula

Variable valuesin cell B11

Left-hand side ofequation in cell B13

NOTE: These cells will be coloredto indicatethatthey are essential for Goal Seek

x

Remember

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

10


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enter formula

Click on cell B13Click on cell B13

Remember

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

10


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enter formula

Type in=AVERAGE(Type in=AVERAGE(

Remember

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

10


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enter formulaRemember

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

10

Highlight cells B2:B11Highlight cells B2:B11


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Preparing the Worksheet for Goal Seekenter formula

Type in) andhitEnterType in) andhitEnter

Remember

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

10


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


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NOTE: The functionAVERAGE entered in cell B13 returns theaverage of the values in cells B2:B11; blank cells are ignored


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Using Goal Seekinvoke Goal Seek

Click onToolsClick onTools


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Click onGoal SeekClick onGoal Seek


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Using Goal Seekcomplete the Goal Seek dialog box

Click on cell B13

Click on cell B13

NOTE: The cell displayed inthe Set cell: box must containthe formula for the left-hand side of the equation(cell B13)


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Click ontheTo value: boxClick ontheTo value: box


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Type in80Type in80

NOTE: The value displayed inthe To value: box must bethe constantonthe right-hand side of the equation(80)


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Click ontheBy changing cell:

box

Click ontheBy changing cell:

box


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Click on cell B11Click on cell B11

NOTE: The cell displayed inthe By changing cell: boxmust be the cell containing variable values (cell B11)


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Using Goal Seekexecute Goal Seek

Click onOKClick onOK


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Using Goal Seekread solution

You needto earn a score of 98onthe 10th quiz to meet your

goal average of 80 points.

NOTE: If the equationhas multiple solutions, Goal Seekusually finds the closest solutiontothe initial variable value.


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Using Goal Seekend execution

Click onOK

Click onOK

Back tostudying!


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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 Solverfor higher precision and/or

equations with multiple variables.

goal seek equations

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