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Replacing Letters with Numbers




 


Videos to help Grade 6 students learn what is an expression and how to build expressions.

New York State Common Core Math Module 4, Grade 6, Lesson 7

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Lesson Plans and Worksheets for Grade 6

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More Lessons for Grade 6

Common Core For Grade 6

Lesson 7 Student Outcomes

Students understand that a letter represents one number in an expression. When that number replaces the letter, the expression can be evaluated to one number.

Example 1

What is the length of one side of this square?
What is the square’s area as a multiplication expression?
What is the formula for the area of a square?
What is the square’s area?

We can count the units. However, look at this other square. Its side length is 23 cm. That is just too many tiny units to draw. What expression can we build to find this square’s area?

What is the area of the square? Use a calculator if you need to.

A letter represents one number in an expression. That number was 3 in our first square and 23 in our second square. When that number replaces the letter, the expression can be evaluated to one number. In our first example, the expression was evaluated to be 9, and in the second example, the expression was evaluated to be 529.

Example 2

The formula A = l × w is an efficient way to find the area of a rectangle without being required to count the area units in a rectangle.

Remember, a letter represents one number in an expression. When that number replaces the letter, the expression can be evaluated to one number.

Example 3

The formula V = l × w × h is a quick way to determine the volume of right rectangular prisms.

Lesson Summary

Expression: An expression is a numerical expression, or it is the result of replacing some (or all) of the numbers in a numerical expression with variables.

There are two ways to build expressions:

1. We can start out with a numerical expression and replace some of the numbers with letters.

2. We can build such expressions from scratch, as in x + x(y - z), and note that if numbers were placed in the expression for the variables x, y, and z, the result would be a numerical expression.






Lesson 7 Examples and Exercises

Exercise 1
Complete the table below for both squares. Note: These drawings are not to scale.

Exercise 2
Exercise 3



 

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You can use the free Mathway calculator and problem solver below to practice Algebra or other math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.


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