Stuck? Start here. Read the steps, try the problem, then check your answer.
I can…
I can evaluate algebraic expressions by substituting values for the variables.
Key words
Variable — A letter that stands for a number that is unknown or can change.
Expression — A math phrase with numbers and letters, but no equal sign.
Evaluate — To find the value by putting numbers in for the letters.
Substitute — To put a number in place of a letter.
Coefficient — The number in front of a letter, like the 3 in 3x.
Like terms — Terms with the same letter raised to the same power, like 2x and 5x.
Steps
Our cost expression is 150 + 12s, where s is the number of speakers.
I want the cost for s = 4 speakers.
I replace s with 4: 150 + 12 × 4.
First I multiply: 12 × 4 = 48.
Then I add: 150 + 48 = 198. So 4 speakers cost $198.
Try it
Evaluate 5(n − 3) + 2 when n = 7.
Check your answer
22
Do the parentheses first: 7 − 3 = 4. Then multiply: 5 × 4 = 20. Then add: 20 + 2 = 22. (If you got 34, you multiplied 5 × 7 first and ignored the parentheses instead of subtracting 3 before multiplying. If you got 20, you found 5(7 − 3) correctly but forgot to add the 2 at the end. If you got 18, you subtracted 2 instead of adding it.)
Sentence starter
I know ___ because ___.
Goal: I can explain my steps using the words variable, expression, evaluate, and substitute.