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.

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?