There are a few tricks to multiply a double digit number by 9, according to different conditions:

- The number is a multiple of 11.
- The tens digit is less than the ones digit by one.
- The tens digit is less than the ones digit.
- The tens digit is greater than the ones digit.

In this page, we are going to discuss about case two, where the number a tens digit less than the ones digit by one.

### Condition:

- The multiplicand is a double digit number where the tens digit is less than the ones digit by one.
- The multiplier is 9.

__Example 1__
34 x 9 = ?

- Let's say the answer is x. x must be a 3 digits number. The digit in the middle must be 0.

- Multiply the first digit of the multiplicand by 9. In this case, 4 x 9 = 36. The product will be the first and third digit of x (see image below.)

**Example 2**

23 x 9 = ?

- 23 x 9 = __ 0 __
- 9 x 3 = 27

Therefore, 23 x 9 = 207

__Example 3__
78 x 9 = ?

- 78 x 9 = __ 0 __
- 9 x 8 = 72

Therefore, 78 x 9 = 702

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