Math Background

Lesson: Multiplication Facts for 2, 5, and 10
Introducing the Concept

It is a good idea to begin by spending some time making connections between addition and the new operation of multiplication. This will allow you to tie what the children have learned to what they are learning in this chapter.

Materials: adding-machine paper and markers in 3 different colors for demonstration; paper and pencil for each child

Preparation: Make a large number line on the adding machine paper from 0 to 100.

Prerequisite Skills and Concepts: Children should know basic addition and subtraction facts and be able to find sums to 100.

Display the large number line on the chalkboard or bulletin board.

  • Say: Today, we will use this number line to investigate certain patterns in numbers. I need a volunteer to show us how to skip count by twos.
    Choose a volunteer to demonstrate the skip counting. As the numbers are found, circle each number with a marker and draw an arrow to the next answer. The volunteer should explain how to get each answer.
  • Ask: What pattern do you see on the number line?
    Children should be able to explain the skipping and counting technique: Start at 0, skip one number, circle number 2, skip number 3, circle number 4, and so on. Repeat until you reach the end of the number line.
  • Ask: How many numbers were circled? How many numbers were skipped?
    Children should respond that 51 numbers were circled and 50 numbers were skipped.
  • Say: Now I need a volunteer to show us how to skip count by fives.
    Choose another volunteer to demonstrate skip counting by fives. Using a different color marker, circle each number announced by the volunteer and draw an arrow to the next answer.
  • Ask: What do you notice about the pattern for skip counting by fives? How is it different from skip counting by twos?
    Be sure children emphasize that every fifth number, instead of every second number, has now been circled.
  • Ask: Why are some numbers circled twice?
    Children should recognize that some numbers (0, 10, 20, 30, 40, 50, and so on — the multiples of 10 up to 100) are circled twice because they are multiples of 2 and of 5.
  • Say: Now I need a volunteer to show us how to skip count by tens.
    Choose another volunteer to demonstrate skip counting by tens. Using the last marker, circle each number announced by the volunteer and draw an arrow to the next answer.
  • Ask: What does our number line show now?
    Children should recognize that the number line shows twos, fives, and tens up to 100. Allow several children to explain what the number line shows.
  • Ask: Which numbers have been circled three times? Why are they circled three times?
    Have children call out the numbers circled three times: 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100. Help children understand that these numbers represent the total number of various groups of twos, fives, or tens.
  • Say: Make a list of the twos at your desks. Then make a list of the fives. Lastly, make a list of the tens.
    When children finish, ask volunteers to read their lists aloud. Record a vertical list for each number on the board.
  • Ask: What patterns do you notice in your lists?
    Encourage children to point out how the tens all end in zeros, the last digit of the fives alternate 5 or 0, and the twos all end in digits 0, 2, 4, 6, or 8. Have children save their lists for reference.
Houghton Mifflin Math Grade 2