Multiplication Center Day

10 min

Narrative

The purpose of this Number Talk is to elicit the strategies and understandings students have for multiplying ​​one- and two-digit numbers, which will be helpful later in this lesson when students multiply within 100.

When students use products they know to find a product they don’t know, they look for and make use of structure (MP7).

Launch

  • Display one expression.
  • “Give me a signal when you have an answer and can explain how you got it.”
  • 1 minute: quiet think time
Teacher Instructions
  • Record answers and strategies.
  • Keep expressions and work displayed.
  • Repeat with each expression.

Student Task

Find the value of each expression mentally.

  • 2×42\times4
  • 5×45\times4
  • 10×410\times4
  • 17×417\times4

Sample Response

  • 8: I counted by 4 twice. I just knew it.
  • 20: I know 5 groups of 4 is 20. I just knew it.
  • 40: It's double 5×45 \times 4. I just knew it.
  • 68: It's the sum of the first three products. 17=10+5+217 = 10 + 5+ 2, so 17×4=(10+5+2)×417 \times 4 = (10 + 5 + 2) \times 4 or (10×4)+(5×4)+(2×4)(10 \times 4) + (5 \times 4) + (2 \times 4), which is 40+20+840 + 20 + 8 or 68.

Synthesis

  • “How did the first 3 expressions help you find the value of the last expression?” (The last expression is 17 groups of 4, which is like 10 groups, 5 groups, and 2 groups of 4 combined. Adding up the value of the first 3 expressions gives you the value of the last expression.)
Standards
Addressing
  • 3.OA.7·Fluently multiply and divide within 100, using strategies such as the relationship between multiplication and division (e.g., knowing that 8 × 5 = 40, one knows 40 ÷ 5 = 8) or properties of operations. By the end of Grade 3, know from memory all products of two one-digit numbers.
  • 3.OA.C.7·Fluently multiply and divide within 100, using strategies such as the relationship between multiplication and division (e.g., knowing that <span class="math">\(8 \times 5 = 40\)</span>, one knows <span class="math">\(40 \div 5 = 8\)</span>) or properties of operations. By the end of Grade 3, know from memory all products of two one-digit numbers.

20 min

15 min