Huh? I think you should revisit that math problem.
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It's correct. When you turn 40 years old, you continue to be 40 all year. It's not the end of being 40 until you turn 41.
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Every century there are celebrations a year early, because it's not the end of the century until XX01 comes around.
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December 31st, 2000 was the last day of the 20th century, not Dec. 31st 1999.
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Therefore the year 2001 was the first year of the 21st century.
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The Fatima apparitions took place in 1917, so October 1918 was the first anniversary, which took a year from that date.
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The apparitions were one year old until they became two years old, which happened from May to October of 1919.
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A century is 100 years, not 99 years and one day.
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