As you recall from ordinary arithmetic, you can solve any problem in addition if you know the sum of any two single-digit numbers. So your only problem in octal addition is to learn the sums of each possible pair of single-dgit octal numbers. Thus you must learn such sums as 68 + 58 = 138, 78 + 78 = 168, 38 + 78 = 128, etc. These may look odd to a person trained in the decimal system, but fortunately there is an easy way to find the sum of any two single-digit octal numbers. Here is the “trick”: To add any two single-digit octal numbers, ass them as decimal numbers; then, if the decimal sum is more than 7, add 2 to get the sum written in octal notation.
