fraction to decimal/3

How do I quickly convert eight-fifths into a decimal?
                            8/5 = 1 + 3/5
                            1 + 3/5 = 1 + 6/10
                            6/10 = .6
                            add .6 back to 1
                            8/5 = 1.6

                                                                            3
Not all numbers ending with nine are divisible by three such that the quotient (result) is a whole number. Two-digit numbers ending with nine and not divisible by three are 19, 29, 49, 59, 79, 89, and so on, and three-digit numbers not divisible by three are 109, 199, and so on. However, if the sum of all the digits in the number is divisible by three, the number is divisible by three. For example, if the number is 657, the number is divisible by three: 6 + 5 + 7 = 18, which is divisible by three. Three makes me think, Trinity.
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Update: Alexander (8) learned this math fact today, 8/4/2022.