Module 3 Lesson12, 13 & 14 Strategies for solving 9s multiplication facts!

Multiply by 8

Skip Count by 6s to 60 … Skip Count by 7s to 70 … Skip Count by 8s to 80 … Skip Count by 9s to 90 … Skip Count

Multiply or Divide by 8 Sprint 2 minutes End

Take from 10! Say the following subtraction sentences in unit form: 20 – 2 (2 tens – 2 ones) = ______ 30 – 3 = ________ 40 – 4 = _____ 50 – 5 = _____ 60 – 6 = _____ 70 – 7 = _____ 80 – 8 = _____ 90 – 9 = _____

A scientist fills 5 test tubes with 9 mL of fresh water in each. She fills another 3 test tubes with 9 mL of salt water in each. How many mL of water does she use in all? Use the break apart and distribute strategy to solve. 9 mL Problem of the Day 5 x 93 x The scientist has 72 mL of water in all.

Use the 9 = 10-1 strategy to solve 9 x n facts

Sometimes we can’t use the commutative property because we don’t know either fact. Let’s use a 10s fact to help solve a 9s fact we don’t know. What’s easier to solve? 9 x 8 10 x 8 How many 8s are in 10 x 8? 10! How many 8s are in 9 x 8? 9!

Use the 9 = 10-1 strategy to solve 9 x n facts Let’s look at it visually!    10 x 8

Use the 9 = 10-1 strategy to solve 9 x n facts Now let’s change the tape diagram to show 9 x 8:   

Use the 9 = 10-1 strategy to solve 9 x n facts    9 x 8 ✗ Write a number sentence that shows the math we just did. 9 x 8= (10 x 8) – (1 x 8) = (80) – (8) =72!!!

Sage and Ava read the same book. It takes Sage 8 minutes to read a chapter, and Ava about 10 minutes. There are 9 chapters in the book. How many fewer minutes does Sage spend reading than Ava? Practice That! 9 x 89 x – 72 = 18 Sage reads 18 minutes less than Ava. 90 – 72 = 18 Sage reads 18 minutes less than Ava.

When we skip count by 9s, we are adding 9 each time. Adding by 9s can be tricky. One strategy for adding by 9 is to add 10 and then subtract one: Identify Patterns in Multiples of 9

Analyze the pattern in the product of the 9s multiplication problems: 2 x 9 = ______ 3 x 9 = ________ 4 x 9 = _____ 5 x 9 = _____ 6 x 9 = _____ 7 x 9 = _____ 8 x 9 = _____ 9 x 9 = _____ What do you notice about the digits in the 10s and the 1s places? Identify Patterns in Multiples of

Next, analyze each PRODUCT. How does the digit in the 10s place relate to the number of groups? 2 x 9 = _____ 3 x 9 = ________ 4 x 9 = _____ 5 x 9 = _____ 6 x 9 = _____ 7 x 9 = _____ 8 x 9 = _____ 9 x 9 = _____ Identify Patterns in Multiples of The digit in the 10s place is one LESS than the number of groups!

Now, with a partner, add together the digits in each product. What pattern do you notice? 2 x 9 = ___________ 3 x 9 = ________ 4 x 9 = _____ 5 x 9 = _____ 6 x 9 = _____ 7 x 9 = _____ 8 x 9 = _____ 9 x 9 = _____ Identify Patterns in Multiples of : 1 +8 = ? ! Check your 9 facts by making sure the products add up to 9!

Do the patterns continue? 9 x 9 = _____10 x 9 = ________ 11 x 9 = ________ 12 x 9 = ________ 13 x 9 = _____14 x 9 = ________ Identify Patterns in Multiples of YES OR NO? Fun math fact: For every 10 & 11 units digits in the tens place (or above) will repeat … then the digits continue to count up. The units in the ones place loop continuously through the digits 0 to 9. How high does the pattern go??

Identify Patterns in Multiples of 9 You can also use your fingers to quickly solve 9s facts up to 10. Put out your hands with all 10 fingers up.

Identify Patterns in Multiples of 9 Let’s solve the fact 3 x 9. Put down the finger that matches the first factor. The number of fingers to the left of the lowered finger are the 10s place. How many fingers? The number of fingers to the right of the lowered finger are the 1s place. How many fingers?

Identify Patterns in Multiples of 9 Let’s solve the fact 7 x 9.

Identify Patterns in Multiples of 9 Let’s solve the fact 9 x 8.

Identify Patterns in Multiples of 9 Let’s solve the fact 9 x 4.

Problem Set