Ed Reingold and Nachum Dershowitz, co-authors of the books Calendrical Calculations and Calendrical Tabulations, determined how often in the period between 1600 and 2400 A.D. Good Friday, Purim, Narouz and the Eid would occur in the same week. The answer is nine times in 800 years. Then they tackled the odds that they would converge on a two-day period. And the total is ... only once: tomorrow [3/21]. More →