After learning the times tables for numbers from 12 to 20 in the previous article, we are going to see the specialty of the biggest one-digit number. Even though 9 is the biggest number, any calculations by 9 can be done easily.
There is one special thing about 9: the digits of the multiples of 9 always add up to 9.
First let us see how to multiply any number from 12 to 20 by 9. There are only two steps involved in this multiplication. Keep in mind that the number of digits in this case is always three.
First Subtract 2 from the number. We have the first two digits of the answer.
To get the last digit complete the total of 9.
Example: 14 x 9
Subtract 2 from 14. 14 – 2 = 12. Our answer is 12--
We know the sum of the digits in the answer has to be 9. Which means 1+2+ -- = 9. The last digit has to be 6.
Answer: 126
This method is real easy as there is no multiplication, only addition and subtraction.
Let us try one more example: 17 x 9
17 – 2 = 15
1 + 5 + -- = 9
Answer: 163
Let us now try the same method for multiplication of any number between 21 to 29 by 9. The steps are the same but in the first step we subtract 3 and then complete the total of 9.
Example: 25 x 9
Subtract 3 from 25. 25 - 3 = 22
Make a total of 9. 2 + 2 + -- = 9. 5 is the missing digit
Answer: 225
For numbers from 11 to 19 we subtract 2 and for numbers from 21 to 29 we subtract 3. The number we subtract makes the difference. That number is one more than the number in the tens place. If we keep that in our mind we can extend this method to other numbers.
Note: For numbers ending in 0, use the 9 times table and include a zero
Tip of the week: Try to draw the pattern of
digital sum for 9.