Evaluate Algebraic Expressions

Students substitute specific values for variables in expressions and compute the result using order of operations. They evaluate expressions involving whole numbers, fractions, and decimals, and interpret the result in context.

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Grade 6 · Expressions and Properties · question 1 of 3

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20 rungs. A star at the top.

a = 5, 2a + 1 =

How it is taught

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To evaluate is to find what an expression is worth.

You substitute a number for each letter.

Then you compute.

Read it: Put the number in

To find 3a + 15 when a = 9, put 9 in place of a. 3a means 3 × 9, which is 27, and 27 + 15 = 42.

Write the expression again with the number in place of the letter: 3 × 9 + 15.
Multiply first: 3 × 9 = 27.
Then add or take away: 27 + 15 = 42.

A number written next to a letter means multiply: 3a is 3 × a.

Multiplying comes before adding, so 3 × 9 is worked out first.

The same expression has a different value for each number put in for a.

Put the number in place of the letter, multiply first, then add or take away.

Reading 3a as 39 when a = 9, and writing 39 + 15 = 54.

3a means 3 × a: 3 × 9 = 27, so 3a + 15 = 27 + 15 = 42.

a = 12, 4a + 18 = ___ — 66. 4 × 12 = 48, and 48 + 18 = 66.

Evaluate 2x + 7 when x = 6

Today we'll evaluate an algebraic expression. That means we plug a number in for the variable and find the value.

Here's our expression: two x plus seven.

The letter x is the variable — it's a placeholder for a number.

We're told that x equals six.

So everywhere we see x, we write six in its place. Two x becomes two times six.

Now we follow the order of operations. Multiplication comes before addition.

Two times six is twelve.

Then twelve plus seven is nineteen.

Grade 6 · Substitute and simplify

When x equals six, two x plus seven equals nineteen. Great work!

What you see

While they climb, your page writes one true line to ask about tonight, and a short note each Sunday.

MayaGrade 3 · Mathematics

Did you know?

A chessboard has 64 squares — share them out between the 8 rows and each row holds exactly 8.

Today’s goal: 1 star — one skill mastered, every rung of its ladder climbed
Climbing now: Divide within 100

An example student.

MayaGrade 3 · Mathematics

Maya earned 2 stars this week — Interpret multiplication as equal groups, which took 6 answers over 3 days before its star landed 3 days ago and Multiply by 6, 7, 8 and 9. Next up: Divide within 100.

An example week.

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Standards

CCSS.6.EE.A.2

Write, read, and evaluate expressions in which letters stand for numbers

CCSS.6.EE.A.2c

Evaluate expressions at specific values of their variables; include expressions that arise from formulas used in real-world problems

Grade 6

Quoted from the Common Core State Standards.

Where this sits

Comes after

Identify Parts of an Algebraic Expression

Leads to

What a star here means

A star here is the top of a twenty-rung ladder, in four blocks of equal length — three of facts and one of the skill used in a real question — where a right answer climbs one rung and a wrong one drops back to the start of the block, never below it. The star is kept for good. How we grade

All of Grade 6

This is one rung of 46 in Grade 6 mathematics, in the order they build on each other.

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