Grade 3-6 Week 5: The “Nines” Patterns: 9x Multiplication Facts
9 times tables are not as difficult as they may first appear, because of the patterns embedded in the number facts. The video includes the following strategies for use with your students:
Teach students to think of ten times, then subtract one set. For example, for “7 x 9″, think about “7 x 10″, then subtract 7.
The multiples of 9 up to 90 exhibit two patterns: the tens go up by ones from 0 to 9, and the ones go down by ones from 9 to 0
The sum of the digits of multiples of 9 up to 90 equals 9.
Thinking of multiples of 9 can be done in two steps: subtract one, that is the number of tens; then find the number which with the tens equals 9, that is the number of ones. For example, “4×9″: the tens will be one less than 4, or 3. The number of ones is the number which added to 3 equals 9, or 6. So 4 x 9 = 36
Finally, there is a finger trick that works up to 9 x 10: Hold up both hands, with palms facing away from you. Imagine the fingers numbered from 1 to 10 from left to right. Whatever number is multiplied by 9, put that finger “down”, or bend it away from you. Now the number of fingers on the left of that finger is the number of tens, and the number to the right is the number of ones.