## Reflection: Multiplying by 9 - Section 1: Warm Up

I was surprised when a student noticed that the digits in the products were "turned around" and that the products of opposite equations had a sum of 99.  For example:

2x8=18, 9x9=81 and 18+81=99

3x9=27, 8x8=72 and 27=72=99

4x9=36, 7x9=63 and 36+63=99

I found this fascinating!

99?
99?

# Multiplying by 9

Unit 10: Fluency to Automoticity
Lesson 2 of 5

## Big Idea: Children will explore the multiples of 9, use patterns in the multiplication equations, and learn a finger trick to become more fluent in quickly multiplying using 9.

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2 teachers like this lesson
Standards:
Subject(s):
Math, multiplication rule, multiplication strategies, counting by, factors, pattern, Fluency (Math)
60 minutes

### Michelle Marcus

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