Lesson plan

Doubling

Teach your students to double two-digit numbers using decomposition as a strategy.
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Students will be able to double two-digit numbers.

(5 minutes)
  • Hold up four objects, like pencils, and tell students that you need double the number of pencils you are holding. *Ask students how many pencils you’ll have if you double the number you are holding (eight).
  • Hold up eight pencils and repeat the question.
  • Hold up 16 pencils and repeat the question. (Note: at this point, students may have a more difficult time answering the question; provide the answer if students are stumped).
  • Tell students that today we are going to be doubling numbers, just like I doubled the number of pencils I was holding. Doubling a number is multiplying it by two.
(10 minutes)
  • On the board write 4 x 2 = 8 and explain, "When I was holding four pencils, and I doubled them, I had eight pencils."
  • Repeat with 8 x 2 = 16 and 16 x 2 = 32.
  • Tell students that doubling is a skill that can be useful in the real world, so today we are going to practice a strategy that will make it easy to think about doubles.
  • Write 35 on the board.
  • Explain that when we double a number, we can decompose, or break apart the number, and double each part. For example, 35 could be decomposed into 30 + 5.
  • Point out that doubling the parts of the numbers (30 x 2) + (5 x 2) is easier to do in our heads than doubling the whole number.
  • Tell students that 30 doubled is 60 and five doubled is 10. So 60 + 10 is the answer.
  • On the board, write 60 + 10 = 70 / 35 x 2=70.
  • Repeat with a second example, like 17.
(15 minutes)
  • Write 23 on the board and have students work with a partner to double it, using decomposition as a strategy.
  • Hand out the Double Bubbles worksheet.
  • Have students complete the worksheet with a partner.
(10 minutes)
  • Hand out the Doubling in the Real World worksheet and instruct students to complete it independently.
  • Circulate as students work and offer support as needed.
  • Go over the worksheets as a class.

Support: Provide simplified practice problems with smaller numbers (i.e. 15, 21, 32).

Enrichment: Have students apply the strategies learned in the lesson to solve word problems.

(5 minutes)
  • Hand out a sticky note to each student (or, alternatively, have students use personal white boards).
  • Write a number on the board, like 48, and instruct students to double it and write their answer on the sticky note.
  • Collect as an exit ticket and check for understanding (Note: if using white boards, have students hold up their answer and scan to check for understanding).
(10 minutes)
  • Ask, "What are some real world situations when you might need to double a number?"
  • Discuss as a class (i.e. making a recipe twice as big; buying two identical items and calculating the cost).

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