Explore

# Multiply Decimals

Teach your students to multiply decimals using the standard algorithm.
Need extra help for EL students? Try the Decimal Product Reasonableness pre-lesson.

Which set of standards are you looking for?

Need extra help for EL students? Try the Decimal Product Reasonableness pre-lesson.

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

The adjustment to the whole group lesson is a modification to differentiate for children who are English learners.
(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 the 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 2,328).
• Point out that both factors are less than one, and say, "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 (2,328) 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 (e.g., 7.96 x 0.4).
• Give students a problem to solve with a partner (e.g., 0.37 x 5.2).
• Give students a "try it" problem to solve independently (e.g., 0.61 x 1.85). Circulate and offer support as needed. Then go over the problem as a class.
(15 minutes)
• Hand out the Multiplying 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 decimal multiplication problem on the board (e.g., 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 "Multiplying Decimals Song" (see related media).