Alternative Algorithms

3rd Grade Math

General Info

Created ByJay Corrigan
SchoolFranklin County Public Schools
LocationWalkersville, MD

About the Lesson

Lesson/UnitAddition and Subtraction

Using the QFT

Place in the Unit/LessonMiddle
Brief description of the unitSolving addition and subtraction problems using strategies related to place value.
Final QFocus

Student Work

Student Questions

Priority questions in bold

  1.  Are those minus signs or negative signs?
  2. Is this one big equation?
  3. Where did 557 come from?
  4. Is that a minus 40 or a negative 40?
  5. How do all the numbers fit together?
  6. What are the two lines?
  7. Why didn’t you borrow?

Teacher Reflections

I did a lesson with a new math qfocus yesterday that was a total winner.  Imagine the subtraction problem 615 – 58 set up in the traditional way, but under the line there are three, stacked numbers, -3, -40, and +600.  Then another line below those three numbers and below that line, 557.  It’s an alternative algorithm for subtraction that deals in numbers rather than in digits (like the traditional algorithm).  The teacher and I were using it to address a 3rd grade Common Core objective related to solving addition and subtraction problems using strategies related to place value, etc.  The teacher is going to use the students’ questions to drive instruction over the next several days, deconstruct the alternative algorithm, and in the process, address lots of math objectives. It was hugely successful!