Lesson 5: Write and Evaluate Algebraic Expressions6.AT.6a

I can…

I can write an algebraic expression for a real situation and evaluate it for a given value of the variable.

Key words

• Write Algebraic Expressions — Translate words or a situation into numbers, variables, and operation symbols.
• Variable — A letter that stands for a number that is unknown or can change.
• Algebraic Expression — A math phrase that has at least one letter.
• Coefficient — The number in front of a letter, like the 3 in 3x.
• Constant — A fixed number in an expression or equation that does not change.
• Like terms — Terms with the same letter raised to the same power, like 2x and 5x.
• Substitute — To replace a variable with a given number before working out the value.
• Evaluate — To find what an expression is worth once every variable has a number, following the order of operations.
• Term — One part of an expression, separated from the others by + or −.

Steps

1. Tickets cost $12 each, plus a flat $50 venue fee. Let t be the number of tickets.
2. "$12 each ticket" means 12 times t, which I write as 12t.
3. The flat fee $50 is added once, so I add 50.
4. I put them together: total revenue = 12t + 50.

Try it

A family orders one $3.50 notebook for each child plus a one-time $6.25 delivery fee. Write the expression for c children, then find the cost for 4 children.

Check your answer

3.50c + 6.25; for c = 4 the cost is $20.25

“Each child” attaches to the variable: 3.50c. The delivery fee is charged once, so it is a constant: 3.50c + 6.25. Substituting c = 4 gives 3.50 × 4 + 6.25 = 14.00 + 6.25 = $20.25.

Sentence starter

I know ___ because ___.

Goal: I can explain my expression using the words variable, term, coefficient, constant, substitute, and evaluate.