The most difficult calendar riddles A list of calendar related questions that are most often answered incorrectly Mathematics quiz Augustus was born on 1 January 10BC. Which birthday did he celebrate at 1 January 10AD?19. There was no year number zero. There were only 1999 years between 1000BC and 1000AD.very hard 39% 191939%202035%212119%80805%Created by: Gizem İsmailoğlu. Statistics based on 13247 answers in 4 languages »math riddles » Typically, how many leap years are in a century?24. The Gregorian Calendar omits 3 leap days every 400 years, omitting February 29 in the 3 century years (integer multiples of 100) that are not also integer multiples of 400. For example, 1600 was a leap year, but 1700, 1800 and 1900 were not. Similarly, 2000 was a leap year, but 2100, 2200, and 2300 will not be.hard 44% 20209%242444%252541%1001004%Created by: ex-terminator. Statistics based on 11119 answers in 2 languages »numbers riddles » How many months have 31 days in them?7. January, March, May, July, August, October and December.hard 57% 5513%6616%7757%8812%Created by: Kasia. Statistics based on 12635 answers in 2 languages »mathematics riddles » Which country started using 7 days in week?Babylon. The seven-day week has deep historical origins in the astrology of Ancient Near East, being approximately a quarter of a lunation. It was (independently) adopted by the Persian Empire, in Judaism and in Hellenistic astrology, and (via Greek transmission) in Gupta India and Tang China.hard 59% Ancient GreeceAncient Greece17%Ancient EgyptAncient Egypt15%Ancient IndiaAncient India7%BabylonBabylon59%Created by: $#O!@B. Statistics based on 2481 answers in 2 languages »history riddles » Which day was the last of the 20th century?31 Dec 2000. There was no year number zero. So, the first century started on 1 Jan 1. Similarly, 21th century started 1 Jan 2001.average 64% 31 Dec 199931 Dec 199926%31 Dec 200031 Dec 200064%31 Dec 200131 Dec 20015%31 Dec 189931 Dec 18993%Created by: Jason Beagley. Statistics based on 15978 answers in 2 languages »time riddles » Who introduced the Gregorian calendar?Pope Gregory XIII. Gregory XIII was pope during the period from 13 May 1572 until 10 April 1585. The Gregorian calendar, also called the Western Calendar, was introduced by him in 1582 with the Bull Inter Gravissimas. The gregorian calendar basically a refinement of the Julian calendar. The Gregorian reform modified the Julian calendar's scheme of leap years, changing the mean length of the calendar year from 365.25 days to 365.2425 days.easy 72% Pope Gregory I, called the GreatPope Gregory I, called the Great17%St. Gregory the IlluminatorSt. Gregory the Illuminator3%Pope Gregory XIIIPope Gregory XIII72%GalileoGalileo6%Created by: Krzysztof Moskal. Statistics based on 7268 answers in 2 languages »popes riddles » Play mathematics quiz and see all the questions.