Video and Examples
Evaluating an expression means to replace the variable with an actual number.
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 
Solution: 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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SelfCheck
Question 1 
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Question 2 
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Question 3 
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