Here is a little trick.

1.) Write a 3-digit number whose digits is decreasing. For example, 421.

2.) Next, reverse the order. The new number now is 124.

3.) Subtract the original number from the reversed number.

421 – 124 = 297

4.) Add the answer in (3) to the reverse of itself.

297 + 792 = 1089.

Let’s try another example.

First step, let’s choose 843.

Next, we reverse its digits: 348.

We subtract: 843 – 348 = 495.

Next, we add 495 to the reverse of itself which is 594.

495 + 594 = 1089.

Let’s try one more example.

First step, let’s choose 762.

Next, we reverse its digits: 267.

We subtract: 762 – 267 = 495

Therefore, 495 + 594 = 1089.

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