April 17, 2017
|
by Sarah Sumnicht

Lesson plan

Multiply Decimals

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Students will be able to multiply decimals using the standard algorithm.

(5 minutes)
  • Review the standard algorithm for multiplication with two-digit whole numbers (i.e. 16 x 74).
  • Tell students, "Today we are going to learn how to multiply decimals."
(10 minutes)
  • Write a decimal multiplication problem on board (i.e. 0.24 x 0.97).
  • Explain that when multiplying decimals, you can ignore the decimal place and multiply using the standard algorithm normally.
  • Demonstrate by multiplying the two numbers (The product is 2328).
  • Point out that both factors are less than one, and ask, "What is one times one? If both factors are less than one, our product should be less than one."
  • Point out the answer you’ve written on the board (2328) and ask, "Is this a logical answer?"
  • Explain that even though you can multiply normally, as you would with whole numbers, you must add the decimal back into the product in the correct place.
  • Tell students that the product will have the same number of digits behind the decimal place as both factors combined.
  • Count the digits behind the decimal in the factors (4). Then add the decimal into the product with the same number of digits behind it (i.e. 0.2328).
(15 minutes)
  • Guide students through another example (i.e. 7.96 x 0.4).
  • Give students a problem to solve with a partner (i.e. 0.37 x 5.2).
  • Give students a "try it" problem to solve independently (i.e. 0.61 x 1.85). Circulate and offer support as needed. Then go over the problem as a class.
(15 minutes)
  • Hand out the How to Multiply Decimals worksheet and go over the example with the class.
  • Instruct students to complete the worksheet independently.
  • Circulate and offer support as needed.
  • Go over the worksheet with the class.

Support:

  • Provide additional examples before assigning independent work.
  • Have students highlight the numbers after the decimal place in the factors and in the product to make sure the decimal is in the correct place.

Enrichment:

  • Have students solve challenge problems with additional place values after the decimal (i.e. 84.0134 x 2.17)
(5 minutes)
  • Hand out a piece of scratch paper to each student.
  • Write a decimals multiplication problem on the board (i.e. 2.38 x 0.91) and have students solve.
  • Collect student work as an exit ticket and check for understanding.
(10 minutes)
  • Teach your students the Multiply Decimals Song (see resources).

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