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Assuming a 90 year spell includes 22 leap years, the number of days is equal to (68 x 365) + (22 x 366) = 24820 + 8052 = 32872 days. If the 90 year spell includes 23 leap years, the number of days is equal to (67 x 365) + (23 x 366) = 24455 + 8418 = 32873 days. 3 people found this useful.
1 This is fairly close, but is wrong by about 1 day every 100 years. 2  So every 100 years we don't have a leap year, and that results in 365.24 days per year (1 day less in 100 year = -0.01 days per year). 3  Closer, but still not accurate enough! 4  So another rule says that every 400 years is a leap year again.