Students will be able to multiply decimals using the standard algorithm.
Introduction (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."
Explicit Instruction/Teacher Modeling (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).
Guided Practice/Interactive Modeling (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.
Independent Working Time (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.
- 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.
- Have students solve challenge problems with additional place values after the decimal (i.e. 84.0134 x 2.17)
Assessment (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.
Review and Closing (10 minutes)
- Teach your students the Multiply Decimals Song (see resources).