Reflection: Connection to Prior Knowledge Big Multiplication and Long Division - Section 1: Do Now


As we were discussing the Do Now problems, one of my students mentioned a multiplication trick that she was taught in elementary school.  This opened the discussion up for sharing tricks.  I realized that even students who were comfortable with their multiplication tables were using some of these tricks to verify their answers.

Here are some of the tricks they shared:

3 - When you multiply a  number by 3, the digits should add up to 3, 6, or 9.

*I asked my students what this trick reminds them of and they were able to recall the divisibility rules from an earlier lesson.  See Divisibility Rules)

9 - When you multiply a number (single digit) by 9, the digits should add up to 9.

Students also had some tricks where they used their fingers, not to count, but to represent numbers.

I shared a trick for multiplying a 2 digit number by 11 that students were really excited about.

Add the digits of the number that is being multiplied by 11 and place them in between the tens and ones place of the number.  For example, 23 times 11 would be 253.

This discussion was a great energizer for students because it gave them an opportunity to share their knowledge/"tricks" with their classmates.

  Multiplication Tricks
  Connection to Prior Knowledge: Multiplication Tricks
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Big Multiplication and Long Division

Unit 8: Algorithms and Decimal Operations
Lesson 3 of 10

Objective: SWBAT review their long division algorithm.

Big Idea: Let the Simpsons help you divide.

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7 teachers like this lesson
Math, division, algorithm
  55 minutes
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