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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.
It has 366 days instead of the normal 365 days. The extra day is added in February, which has 29 days instead of the normal 28 days. Leap years occur every 4 years. 2016 is a leap year and so is 2020.