self Maths Puzzle

f D = the day (1-366) in year Y, then the day of the week can be calculated using

d = D+Y+(Y-1)/4 - (Y-1)/100 + (Y-1)/400 mod7

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self Other Question

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Pick 3 digits (not zero) and make 6 2-digit numbers from them. Add up all these numbers, add up all the original digits and divide the first total by the second.