Multiplying with a decimal number with 1 or 2 decimal places

Students learn to multiply with a decimal number with 1 or 2 decimal places.

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The students learn to multiply with a decimal number with 1 or 2 decimal places.

CCSS.Math.Content.5.NBT.B.7

Students will be able to multiply a decimal number with 1 or 2 decimal places with another number.

You have the students write down a decimal number with one or two decimal places. Next everyone looks for a classmate with the same number of decimal numbers and they add the numbers they have written down together.

You explain that you can calculate a multiplication problem with a decimal number using different methods. Explain the first method. For this you must first count the number of digits that are after the decimal point. Then you calculate the problem, in which you have removed the decimal point. After that you explain that you must add the decimal point back on to your answer. If there was one digit after the decimal point, then there must be one digit after the decimal point in your answer. After this you explain the other method. First you solve the problem using only the numbers in front of the decimal point. Then you calculate the problem with the number after the decimal point. You add the outcomes of both problems together to get your answer. Next you have the students practice multiplying decimal numbers. Ask which method they used to solve the problems. Ask the students how they would solve a problem in which the decimal number has two decimal places. Then explain that you can solve this in the same way that they solved problems with a decimal number with one decimal place. Have the students practice multiplying with a decimal number with two decimal places. Finally you show how you can solve a story problem. You have the students determine what type of problem it is, which numbers you need to make the problem and the you solve the problem together. After this, have the students solve another story problem on their own.

Check whether the students can multiply with a decimal number with one or two decimal places with the following questions:

- How do you solve a multiplication problem with a decimal number with one or two decimal places?

- How do you solve the following problem: 4 × 3.7?

The students test their understanding of multiplying with a decimal number with 1 or 2 decimal places by completing ten exercises. For some of the exercises they must solve multiplication problems, either with a choice of possible answers or by providing the answer on their own. For other exercises, the students must determine if the answer given is correct or not. Other exercises are story problems.

You discuss once again with the students that it is useful to be able to multiply with decimal numbers with one or two decimal places. Ask the students how they would solve this type of problem. To check if the students can multiply with a decimal number with one or two decimal places, show them a few problems. They must determine if the answer given is correct or not. If the answer is incorrect, they must give the correct answer. They also solve a problem with a decimal number with two decimal places.

When students have difficulty with multiplying with a decimal number with one or two decimal places, you can show them the different methods or how they can solve this type of problem again. Solve a problem together, step by step.

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