Writing and Evaluating Variable Expressions

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Writing and Evaluating Variable Expressions
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Section 1.1 Variables in Algebra
Welcome to todays lesson. Before we begin, we
must know the definitions...
What is a variable? What is a value?
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Section 1.1 Variables in Algebra
Variable expression A collections of numbers,
variables, and operations Variable
Expression Meaning
Operation 8y
8 times y
multiplication
10
divided by b division
7 x
7 plus x
addition 5 - t
5 minus t
subtraction
10 b
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Section 1.1 Variables in Algebra
Evaluating the expression Replacing the variable
in an expression by a number The resulting
number is the value of the expression
Examples Evaluate the expression 8y when y
2 Answer 8y
8(2) 16 Evaluate the expression 7 b when
b 6 Answer 7 b 7
6 13
Simon Cowel is pleasantly surprised that he
enjoys evaluating expressions.
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Section 1.1 Variables in Algebra
HEY DAWG, Define these terms Unit analysis
Verbal model
In real-life problems... We translate the words
of the problem into math We also use the units
of the variables in the problems to help
determine the units for the answer.
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Solution Let's represent the problem in math
terms d distance 80 miles
t time of 2 hours .
Substitute the values of d and t into the
equation
d
t
Speed
Distance d 80miles 40 miles Time
t 2 hours hours
Average speed is 40mph


Average speed

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Make it REAL...Using Unit Analysis
In real-life problems... use the
units of each variable...
to determine the units for the answer!
Hints... Use variables and units (rate 6
miles/hour , distance 10.5 miles) The question
is "How long..." This answer should be a unit of
time, which can be hours Multiply or divide the
variable that you know (with units) to get hours
in the numerator, and everything else cancels out
Answer Time distance 10.5miles
1.75 hours
rate 6 miles/hour
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Homework Chapter 1 Connections to Algebra