Math and Christmas
One day, five siblings wrote down the date of the first Christmas in their lives as well as its corresponding days of the week. Here are their answers:
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Charles: 25 December 1991 (Monday)
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Darius: 25 December 1994 (Tuesday)
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Brenda: 25 December 1996 (Wednesday)
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Alfred: 25 December 1999 (Thursday)
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Eric: 25 December 2000 (Friday)
ONE of them is correct. Who???
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1 solution
To determine the day of the week based on any give date day/month/year we simply follow the formula d + m + y + 4 y + c , and the result is then calculated in mod7 . In the formula, d is the day of the month, m is the number of the month in the month's table, y are the last two digits of the year's number, c is the century's number. The result of such formula are numbers from 0 to 6, where 0 = Saturday and 6 = Friday.