Substitution

Substitution

6.EE.1.2c I will be able to evaluate expressions in which letters stand for numbers.

RECALL

An algebraic expression contains one or more variables. You can substitute a number for that variable and then find the value of the expression. This is called evaluating the expression.

Evaluate the expression

 $x-9$ ; x = 15

• Step 1: Substitute- replace the variable with the value 15 in the expression.

• Step 2: Evaluate the new expression  $15-9$  

• When x = 15, x - 9 is 6. 

Evaluate the expression

 $4x$ ; x = 8

• Step 1: Substitute- replace the variable with the value 8 in the expression.

• Step 2: Evaluate the new expression  $4\cdot8$  

• When x = 8, 4x is 32. 

Let's Review: Order of Operations

• Step 1: Perform operations in (parentheses) first.

• Step 2: Evaluate exponents

• Step 3: Multiply and divide from left to right

• Step 4: Add and Subtract from left to right

Multiple Choice

Given the expression

 $6-5+3$  
which operation do we do first

• add

• subtract

Evaluate the expression

 $3a-b;\ a=4,\ b=6$ 

• Step 1: Substitute- replace the variables with numbers in the expression. a=4 and b=6

• Step 2: Evaluate the new expression  $3\left(4\right)-6$  

• The value of the expression when a=4 and b=6 is 6. 

Evaluate the expression

 $ab-c\ ;\ a=3,\ b=4,\ and\ c=6$ 

• Step 1: Substitute- replace the variables with numbers in the expression. a=3 and b=4 and c=6

• Step 2: Evaluate the new expression  $\left(3\right)\left(4\right)-6$  

• The value of the expression when a=3, b=4, and c=6 is 6.