Math Background

Lesson: Multidigit by One-Digit Multiplication
Introducing the Concept

Introduce students to this topic by showing them how they can use the properties and rules they learned with basic multiplication facts for multiplying with two-and three-digit factors.

Materials: none

Preparation: none

Prerequisite Skills and Background: Students should know the basic multiplication facts.

  • Ask: When 0 is a factor in a multiplication sentence, what is the product?
    Students should know that the product is always 0.
  • Ask: What is the product of 0 and 58? (0) What is the product of 967 and 0? (0) What is the product of 0 and $3.98? (0)
    Have students suggest other examples of multiplying with 0 and a two- or three-digit number as the factors.
  • Ask: When 1 is a factor in a multiplication sentence, what is the product?
    Students should know that the product is always equal to the other factor.
  • Ask: What is the product of 77 and 1? (77) What is the product of 1 and 365? (365) What is the product of $9.61 and 1? ($9.61)
    Have students suggest other examples of multiplying with 1 and a two- or three-digit number as the factors.
  • Ask: When a factor is doubled, what happens to the product?
    Students should recall that the product is doubled.
  • Write 7 x 3 = n on the board.
  • Ask: What is the product of 7 and 3? (21)
    Replace n with 21.
  • Ask: What number is double 7? (14)
  • Write 14 x 3 = n on the board.
  • Ask: What is double 21? (42) So what is the product of 14 and 3? (42)
    Replace n with 42.
  • Write 16 x 5 = n on the board.
  • Ask: How can we use doubles to find the product of 16 and 5?
    Elicit from students that 16 is double 8, 8 x 5 = 40, 80 is double 40, so 16 x 5 = 80. Replace n with 80.
  • Ask: What does the Commutative Property of Multiplication tell us?
    Changing the order of the factors does not change the product.
  • Write 5 x 16 = n on the board.
  • Ask: What is the product of 5 and 16? (80)
    Replace n with 80.
  • Provide students with additional examples of using doubles and the Commutative Property to multiply with two- and three-digit factors. This will help students see that multiplying with two- and three-digit factors is really not a new concept; it is just building on previously learned skills.
Houghton Mifflin Math Grade 3