goal seek equations
TRANSCRIPT
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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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Preparing the Worksheet for Goal Seek
enter labels and constants
Enter labels in cellsA1:A13 andB1
Enter labels in cellsA1:A13 andB1
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Preparing the Worksheet for Goal Seek
enter labels and constants
NOTE: These labels are notessential for the use of Goal Seek
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Preparing the Worksheet for Goal Seek
enter labels and constants
Enter constants incells B2:B10
Enter constants incells B2:B10
Remember
74
8
7266828468788890Score
97654321Quiz
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Preparing the Worksheet for Goal Seek
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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Preparing the Worksheet for Goal Seek
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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Preparing the Worksheet for Goal Seek
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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Preparing the Worksheet for Goal Seek
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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Preparing the Worksheet for Goal Seekenter formula
NOTE:Alternative formula for cell B13:=(B2+ B3+ B4+ B5+ B6+ B7+ B8+ B9+ B10+ B11)/10
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Preparing the Worksheet for Goal Seekenter formula
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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Using Goal Seekinvoke Goal Seek
Click onGoal SeekClick onGoal Seek
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Using Goal Seekinvoke Goal 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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Using Goal Seekcomplete the Goal Seek dialog box
Click ontheTo value: boxClick ontheTo value: box
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Using Goal Seekcomplete the Goal Seek dialog box
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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Using Goal Seekcomplete the Goal Seek dialog box
Click ontheBy changing cell:
box
Click ontheBy changing cell:
box
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Using Goal Seekcomplete the Goal Seek dialog box
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.