In the previous post, we have learned about the **1089 math trick**. In this post, we are going to learn why the math trick works. Recall that the math trick has the following steps:

1.) Write a 3-digit number where the digits are decreasing.

2.) Reverse the digits of the number.

3.) Subtract the result from (2) from the original number in (1).

A 3-digit number, write the digits abc has value 100a + 10b + c. For example, the number with digits 347 has value 100(3) + 10(4) + 7.

In Step 1, we write the number 100a + 10b + c where a >= b and b >= c.

In Step 2, if we reverse the digits, it will become 100c + 10b + a. Continue reading