Create Word Problems

10 min

Narrative

The purpose of this Number Talk is to elicit the strategies and understandings students have for subtracting multi-digit numbers when the minuend is a multiple of 100. These understandings help students develop fluency and will be helpful later in this lesson when students will need to interpret student work and solve word problems that involve multi-digit numbers. 

Launch

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

Student Task

Find the value of each expression mentally.

  • 5,000−4035,000 - 403
  • 5,300−4735,300 - 473
  • 25,300−49325,300 - 493
  • 26,000−1,49326,000 - 1,493

Sample Response

  • 4,597: I know that 5,000−400=4,6005,000 - 400 = 4,600 and 4,600−3=4,5974,600 - 3 = 4,597.
  • 4,827:
    • We can add 300 to our result before (5,300 is 300 more than 5,000) to get 4,897 and subtract 70 from it (473 is 70 more than 403) to get 4,827.
    • 5,300−400=4,9005,300 - 400 = 4,900. Subtracting 70 from 4,900 gives 4,830 and subtracting 3 from 4,830 gives 4,827.
  • 24,807: We can add 20,000 to the previous result (25,300 is 20,000 more than 5,300), and then subtract 20 (493 is 20 more than 473).4,827+20,000−20=24,8074,827 + 20,000 - 20 = 24,807
  • 24,507: I know 1,493 is 7 away from 1,500 and 26,000−1,50026,000 - 1,500 is 24,500, so 26,000−1,49326,000 - 1,493 is 7 more than 24,500.
Activity Synthesis (Teacher Notes)
  • “Did you find yourself always using an earlier expression to help you find the value of a new expression? Did you find yourself switching strategies at times?”
  • “Which expression did you find most challenging to reason about?” (Sample response: 26,000−1,49326,000-1,493 because there were many zeros in the number being subtracted from.)
Standards
Addressing
  • 4.NBT.5·Multiply a whole number of up to four digits by a one-digit whole number, and multiply two two-digit numbers, using strategies based on place value and the properties of operations. Illustrate and explain the calculation by using equations, rectangular arrays, and/or area models.
  • 4.NBT.B·Use place value understanding and properties of operations to perform multi-digit arithmetic.
  • 4.NBT.B·Use place value understanding and properties of operations to perform multi-digit arithmetic.
  • 4.NBT.B.5·Multiply a whole number of up to four digits by a one-digit whole number, and multiply two two-digit numbers, using strategies based on place value and the properties of operations. Illustrate and explain the calculation by using equations, rectangular arrays, and/or area models.

15 min

20 min