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

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Denise Sakai Troxell (2000) 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 quizzes are given in the table below. Quiz123456789 Score908878688482667472 What score do you need to earn on the 10 th 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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Denise Sakai Troxell (2000) You are looking for x = score on 10 th 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 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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Denise Sakai Troxell (2000) Preparing the Worksheet for Goal Seek start with a blank sheet

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Denise Sakai Troxell (2000) Preparing the Worksheet for Goal Seek enter labels and constants Enter labels in cells A1:A13 and B1

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Denise Sakai Troxell (2000) Preparing the Worksheet for Goal Seek enter labels and constants NOTE: These labels are not essential for the use of Goal Seek

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Denise Sakai Troxell (2000) Preparing the Worksheet for Goal Seek enter labels and constants Enter constants in cells B2:B10 Remember… 74 8 7266828468788890Score 97654321Quiz

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Denise Sakai Troxell (2000) Preparing the Worksheet for Goal Seek enter formula Variable values in cell B11 Left-hand side of equation in cell B13 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

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Denise Sakai Troxell (2000) Preparing the Worksheet for Goal Seek enter formula Click on cell B13 Remember… 90 + 88 + 78 + 68 + 84 + 82 + 66 + 74 + 72 + x = 80 10

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Denise Sakai Troxell (2000) Preparing the Worksheet for Goal Seek enter formula Type in =AVERAGE( Remember… 90 + 88 + 78 + 68 + 84 + 82 + 66 + 74 + 72 + x = 80 10

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Denise Sakai Troxell (2000) Preparing the Worksheet for Goal Seek enter formula Remember… 90 + 88 + 78 + 68 + 84 + 82 + 66 + 74 + 72 + x = 80 10 Highlight cells B2:B11

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Denise Sakai Troxell (2000) Preparing the Worksheet for Goal Seek enter formula Type in ) and hit Enter Remember… 90 + 88 + 78 + 68 + 84 + 82 + 66 + 74 + 72 + x = 80 10

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Denise Sakai Troxell (2000) Preparing the Worksheet for Goal Seek enter formula NOTE: Alternative formula for cell B13: =(B2+ B3+ B4+ B5+ B6+ B7+ B8+ B9+ B10+ B11)/10

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Denise Sakai Troxell (2000) Preparing the Worksheet for Goal Seek enter formula NOTE: The function AVERAGE entered in cell B13 returns the average of the values in cells B2:B11; blank cells are ignored

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Denise Sakai Troxell (2000) Using Goal Seek invoke Goal Seek Click on Tools

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Denise Sakai Troxell (2000) Using Goal Seek invoke Goal Seek Click on Goal Seek

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Denise Sakai Troxell (2000) Using Goal Seek invoke Goal Seek

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Denise Sakai Troxell (2000) Using Goal Seek complete the Goal Seek dialog box Click on 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)

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Denise Sakai Troxell (2000) Using Goal Seek complete the Goal Seek dialog box Click on the To value: box

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Denise Sakai Troxell (2000) Using Goal Seek complete the Goal Seek dialog box Type in 80 NOTE: The value displayed in the To value: box must be the constant on the right-hand side of the equation (80)

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Denise Sakai Troxell (2000) Using Goal Seek complete the Goal Seek dialog box Click on the By changing cell: box

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Denise Sakai Troxell (2000) Using Goal Seek complete the Goal Seek dialog box Click on cell B11 NOTE: The cell displayed in the By changing cell: box must be the cell containing variable values (cell B11)

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Denise Sakai Troxell (2000) Using Goal Seek execute Goal Seek Click on OK

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Denise Sakai Troxell (2000) Using Goal Seek read solution You need to earn a score of 98 on the 10 th 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.

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Denise Sakai Troxell (2000) Using Goal Seek end execution Click on OK Back to studying!

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Denise Sakai Troxell (2000) Final Comments Goal 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.

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