Determine difference between decimal numbers with 1 or 2 decimals places

General

Students learn to determine difference between two decimal numbers with 1 or 2 decimal places.

Common core standard(s)

6.NS.B.3

Relevance

It is useful to be able to determine the difference, so you can tell which number is greater or less than the other.

Introduction

A few objects are shown on the interactive whiteboard as well as a few decimal numbers. Have students match the numbers to the objects. Tell students that they are trying to estimate about how much a decimal number is. They can sort it out in pairs first, and then discuss as a class.

Development

Explain to students that if you want to determine the difference between two numbers, you look to see how much more or less one number is than the other. Explain that you can use the number line to determine what the difference between two numbers is, by adding to one number to reach the other. You show this in three steps. Step 1 is to count to the next whole number, step 2 is to go to the next whole number, and step 3 is to add to the decimal number. Tell students that this is adding to one number to reach the other. Explain that you can also make a subtraction problem. Demonstrate this to students by using a subtraction problem with 1 decimal place, and then with a subtraction problem with 2 decimal places. Discuss with students how they can determine the difference. Then you tell students how to determine difference in a story problem. Explain that you must first determine what kind of problem it is, determine which numbers are important, then to say or write the problem, and finally to solve the problem. Solve one story problem as a class and then have students solve the next story problem individually or in pairs.

To check that students are able to determine difference with decimal numbers with 1 or 2 decimal places, you can ask the following questions:
- How can you determine difference between two decimal numbers?
- Which subtraction problem can you make to determine the difference between 53.26 and 68.35?
- What steps do you take to solve a story problem?

Guided practice

Students are asked to determine the difference between two given numbers with 1 or 2 decimal places. They are also asked to complete the a table with two numbers in which we want to know the difference between the given numbers. Students are also asked to solve story problems.

Closing

Repeat the learning goal with the students. The interactive whiteboard has a table with prices from Store A and Store B. Ask students to determine the difference between the prices of the two stores. Ask students to explain their strategy.

Teaching tips

Students who have difficulty determining difference can be supported by making use of the number line. Have them first jump from the decimal number to a whole number, from the round number to the next whole number, and then jump to the decimal number again.