Video and Examples

Evaluating an expression means to replace the variable with an actual number.

Suppose you have the variable expression \frac{3m-2}{8}

This expressions means "I'm thinking of a number that is multiplied by 3, then subtracted by 2, and finally divided by 8."

Evaluating an expression means replacing the variable with an actual number. For example, if m = 6, then \frac{3m-2}{8}=\frac{3\cdot~6-2}{8}=\frac{18-2}{8}=\frac{16}{8}=2


Example 1

Martha went to the hobby store and purchased two bags of marbles plus 3 extra marbles.

We don't know the number of marbles in each bag, so all we can say is that she bought 2x + 3 marbles. 

If we are told there are 42 marbles in each of Martha's bags, then we can substitute 42 for the x in the variable expression.

2x + 3 ------> 2(42) + 3 = 84 + 3 = 87 marbles

Martha bought 87 marbles.


Example 2

Evaluate 2x+3 if x = 17.


Replace the variable with 17 and then simplify.


Example 3

Jenny was filling bottles from a tank of water. When she had filled four bottles with water, 1 cup of water was left in the tank. How much water is in the tank?

The variable expression for this situation is 4c + 1, where c represents the number of cups in each bottle.

If c = 6, how many cups of water are in the tank?


Example 4

If a = 3, b = 6, and c = 4 evaluate each of the following expressions.




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Question 1

Evaluate 4x-6 for x=4.

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Question 2

Evaluate 6x+2x for x=3.

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Question 3

Evaluate \frac{39}{x}+5y for x=3\mbox{ and }y=5

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Last modified: Thursday, 16 April 2020, 12:37 PM