Select a number with different 1st and 3rd digits.

Reverse the digits.

Subtract the smaller digit from the larger.

Reverse the digits of this answer.

Add these two numbers.

Subtract a number from this sum.

The final answer will be 1089 minus whatever number you choose in step 6!

Example:

For the last step you say to subtract 22.

The answer is: 1089 - 22 = 1067.

See the pattern?

For the last step you say to subtract 101.

The answer is: 1089 - 101 = 988.

Each time, change the number you select for the last step - just select one that
is easy to subtract from 1089. Then your answers will be immediate and correct.