June 5, 2020 1 min to read

Find the sum of two digits number

Tìm tổng các số có hai chữ số

• Theory

  It's great if you can add numbers quickly in the traditional way. Now consider the following quick way\[\overline{ab}+\overline{cd}= 10 \times (a+c) + (b+d)\].

  In words, try adding the tens, then multiply them by ten, and add the result to the sum of the unit digits.

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