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jmc

algebra junior

Problem

The sum of the digits of a two-digit number is The difference between the number and the number with its digits reversed is What is the sum of the original number and the number with its digits reversed?
Solution
The two digit number can be represented as where and are digits, with We are given that the sum of the digits is so If we reverse the digits of this number, we have We are given that the difference is but we don't know if the original number or if the number with its digits reversed is greater. We can show this as such: However, it doesn't matter which of the two numbers is greater, since we wish to find their sum. So, without loss of generality, we will let the first number be the larger of the two. This means that so we can get rid of the absolute values in our last equation to obtain equivalent to

We now have two equations in two variables: and Adding the two, we obtain so Subtracting, we obtain so Thus, the original number is and our answer is

OR

As before, the two digit number can be expressed as and the number with its digits reversed is We want to find the sum of these two numbers, which is We are given that the sum of the digits is so Since all we want is we can substitute for to obtain our answer of
Final answer
143