Modeling Relationships with Variables 91007

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Modeling Relationships with Variables9/10/07

• A variable a symbol, usually a letter, that
  takes the place of one or more numbers.
• An algebraic expression a mathematical phrase
  that can include numbers, variables, and
  operation signs.
• Sometimes called variable expressions.

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Writing an Algebraic Expression

• More than addition
• Less than, difference of subtraction
• Product of multiplication
• Quotient of division

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Writing an Algebraic Expression

• Write an Algebraic Expression for each phrase.
• Eight more than n.
• - add the first number, eight, to the second
  number, n.
• Answer n 8
• b. The difference of n and 8.
• - subtract 8 from n.
• Answer n 8
• The product of 7 and n.
• - multiply 7 and n.
• Answer 7n
• The quotient of n and 7.
• - divide n by 7.
• Answer

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Writing an Algebraic Expression Cont.

• Define a variable and write an algebraic
  expression for each phrase.
• a. Two times a number plus nine.
• Define Let x the number
• Answer 2x 9
• b. Five less than three times a number.
• Define Let m the number
• Answer 3m 5

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More Practice!!!! P. 6 1 7 odd

• Write an algebraic expression for each phrase.
• 1. 4 more than p.
• 4 p
• 3. 12 minus m.
• 12 - m
• 5. The quotient of n and 8.
• 7. 23 less than x.
• x 23

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More Practice (Cont.)!!!! P. 6 9 15 odd

• Define a variable and write an expression for
  each phrase.
• 9. 2 more than twice a number.
• Let m a number
• 2m 2
• 11.9 minus a number.
• Let n a number
• 9 - n
• 13. The product of 5 and a number.
• Let k a number
• 5 k
• 15. The quotient of a number and 6.
• Let s a number

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Modeling Relationships with Equations and Formulas

• Use algebraic expressions to write an equation.
• An equation a mathematical sentence that uses
  an equal sign.
• If an equation is true, the two expressions on
  either side of the equal sign represent the same
  value.

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Modeling Relationships with Equations and
Formulas (cont.)

• Example.
• CDs cost 10 each. Write an equation for the
  total cost of a given number of CDs.
• Let n number of CDs bought
• Let c the total cost
• ANSWER c 10 n
• c 10 n

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Homework!!!

• Textbook p. 6 2 16 even