Evaluate algebraic expressions

You can evaluate algebraic expressions when you substitute numbers for the variables in algebraic expressions and then follow the order of operations.

Example #1

Evaluate 2a + b + 1 for a = 3 and b = 5

Substitute 3 for a and 5 for b

2a + b + 1 = 2×3 + 5 + 1

Multiply first

2a + b + 1 = 6 + 5 + 1

Add from left to right

2a + b + 1 = 11 + 1

Add

2a + b + 1 = 12

Example #2

Evaluate a + 4b - ab for a = 2 and b = -1

Substitute 2 for a and -1 for b

a + 4b - ab = 2 + 4(-1) - (2)(-1)

Multiply first

a + 4b - ab = 2 + -4 - (-2)

Add the opposite when subtracting

a + 4b - ab = 2 + -4 + 2

Add from left to right

a + 4b - ab = -2 + 2

Add

a + 4b - ab = 0 

Example #3

Evaluate a + 4a ÷ b - 3b for a = 5 and b = -4

Substitute 5 for a and -4 for b

a + 4a ÷ b - 3b5 + 4(5) ÷ -4 - 3(-4)

Multiply first

a + 4a ÷ b - 3b = 5 + 20 ÷ -4 - 12

Divide

a + 4a ÷ b - 3b = 5 + -5 - 12

Add the opposite when subtracting

a + 4a ÷ b - 3b = 5 + -5 + -12

Add from left to right

a + 4a ÷ b - 3b = 0 + -12

Add

a + 4a ÷ b - 3b = -12

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