This module introduces a learning tool or trick to help solve a number multiplied by 9 in a cool way. While the trick is simple, it is great for young learners and will get them excited to show it to other kids.
The cards contains visual pictures of the trick and also have tools to speed up the calculation.
OVERVIEW & PURPOSE
Week 5 of the 3rd Grade CountFast program focuses on strategies to add, subtract, and multiply with the digit 9. Spend 15 minutes each day on one of the activities listed in this module. Card decks should go home with students each day for additional practice with a parent at home. Each week, a new deck is introduced, and the previous deck is for the student to keep at home for continued practice.
- NCTM Standard: develop a sense of whole numbers and represent and use them in flexible ways, including relating, composing, and decomposing numbers
Apply properties of operations as strategies to multiply and divide.
- Mentally add and subtract with the number nine.
- Mentally multiply one and two-digit numbers by nine.
- One CountFast 9 card deck for each student. This deck is for school and home use. Discuss routine and expectations for taking home the deck and returning it to school each day.
- One writing utensil per student, optional per teacher plans.
CountFast 9 Pack – Day 1
Teacher Model/Direct: Use the yellow cards from the deck. Teach students that the fastest way to add 9 to any number is to think of 9 as being one less than 10. Add ten to the original number, and then back up one spot (in a negative direction) on the number line. For example, to add 18 + 9, first realize that 18 + 10 is 28, then back up one spot on the number line, which would be 27 for a final answer. Practice with the class using the yellow cards.
Student Activity: Give each student a deck and ask them to take out the yellow cards. Working with a partner, take turns holding up the cards for the partner to add 9 using the strategy from the lesson.
Home Activity: Students will take home the deck and the “CountFast Home Connection” letter. Students will review the strategy for adding 9 to a number. Parents can record how quickly the child adds all of the yellow cards correctly.
CountFast 9 Pack – Day 2
Teacher Model/Direct: Using the same procedure as Day 1, introduce the blue cards in the deck. Today we will be subtracting 9 from a number using the same idea that 9 is the same as 10 – 1. Subtract 10 from the original number, and then move up one place on the number line. For example, solve 23 – 9 by first subtracting 10. This puts you at 13. Then move up (in a positive direction) on the number line one spot, which gives the final answer of 24. Practice with the class using the blue cards.
Student Activity: Students should work with a partner, using the blue cards, to practice subtracting 9 from any number. If time allows, review the yellow cards and adding 9 to a number.
Home Activity: Students will review the strategy for subtracting 9 from a number. Parents will use the blue cards with child and record how quickly the child answers all cards correctly each round.
CountFast 9 Pack – Day 3
Teacher Model/Direct: Use the pink cards from the deck. Today, show students the ‘finger trick’ for multiplying a single-digit number by nine. Model the technique several times with the class, then have students look at the pink cards to see that the pictures are the same as the examples you modeled for them. (Holding both hands up in front of you, think about ‘reading’ the fingers as 1 through 10, going from left to right. Hold down the finger that 9 is being multiplied by – for example, 9 X 3 – hold down the third finger. The fingers on the left of the one held down represent the ‘tens’ number of the answer. The fingers on the right represent the ‘ones’ digit of the answer. For 9 X 3, there are 2 fingers on the left, and 7 on the right, giving the answer of 27.)
Student Activity: With a partner, practice using the ‘finger trick’ method of multiplying a single-digit number by nine. If time allows, review the strategies for adding and subtracting 9 with the yellow and blue cards.
Home Activity: Students will share and practice the ‘finger trick’ method of multiplying by nine with parents.
CountFast 9 – Day 4
Teacher Model/Direct: Use the green cards in the deck for today’s lesson. Review how to quickly add, subtract, and multiply by nine. Then introduce the strategy to multiply two-digit numbers by nine. The quick way to mentally multiply by 9 is to multiply the original number by 10 (by simply adding a zero to the original number) and then subtract the original number to get the final answer. For example, 15 X 9 is solved quickly by first multiplying 15 X 10 to get 150, and then subtracting 15 from 150 to get a final answer of 135.
Student Activity: Students will work with partner using green cards to use the lesson strategy to multiply double-digit numbers by nine. If time allows, review the other cards from previous lessons this week.
Home Activity: Students will share and practice the strategy for multiplying a two-digit number by nine with parents. Parents can track the speed in which the child works through all of the green cards each round of practice.
CountFast 9 – Day 5
Teacher Model/Direct: Today, review with students the strategies for adding/subtracting 9. Also review the finger method of multiplying a single-digit number by 9, and the strategy for multiplying a two-digit number by nine. This can be made more challenging by shuffling all of the cards in the deck to that students have to really think about what operation is on the card.
Student Activity: With a partner, shuffle the deck and take turns answering the problems on the cards using the strategies for working with 9.
Home Activity: Students will review this week’s strategies for working with 9.