Jul 15, 2011

Rare months? NOT!

(Pic Courtesy: walyou.com)
From being amusing and funny, it has gone down to downright irritating to read and receive via e-mail and SMS, news that a particular month is rarely unique. An example is this month itself - July 2011 having an once-in-823-years-occurrence of 5 each Fri, Sat & Sundays. How more absurd can it get? A little application of school maths would have prevented the gossip mongers from making a fool of themselves.

There are 7 months in a year that have 31 days. After subtracting 4x7=28 days, u get 3 days which get repeated for the 5th time. Now, for any combination of Fri, Sat & Sun or Sat, Sun & Mon, the first day in the sequence also has to be the first day of the month. The probability that any of the 7 days of the week is the first day of any month is 1/7. Usually, one particular date on the next year falls on the next day. That is bcos, every 'normal' year has 365 days, which is 52 weeks PLUS one day. Some of you would have noticed that if your birthday was on Sat this year, it would be on Sun the next year, if there is no 'Feb 29' in between. In that case, it is 52 weeks + 2 days.

So, for any particular month, one can say that, usually once in 7 years, most of the Sun-Sat w'd be the first days of the month. But not all days, because of the leap year problem. Whenever that month appears for the first time after any Feb 29, the days get pushed by 2. In any case, here are the facts: Of the 7 months having 31 days, only 2 will have the same day pattern from 1st to 31st: Jan & Oct in a normal year, and Jan & July in a leap year. It means that there are 6 different patterns out of the possible 7. It also implies that, the occurrences of 3 Fri, Sat & Sun or Sat, Sun & Mon are very common. Also, leap year or not, every one of these 7 months w'd have gone through a particular Sun-Sat pattern atleast once in a decade.

On the other hand, 11th of Nov this year will be a unique occurrence, which happens once in 100 years. 11-11-11 wont be possible until 2111.


Anonymous said...

Wow. Superb.. Ppl mostly ignore such emails.. This proves u r a great scientist.. Will call n ask doubts on this :)

Raju said...

Ani, :) thank you. Ya pl call when u r free. Long time since we spoke. Looking forward to talk to u..

Me too said...

Tell me about it!! Apart from unique days, 2 moons / 2 suns in the sky kinds vera(though now there is this new 2 moons theory -http://www.bbc.co.uk/news/science-environment-14391929)!!

When I was working, we had to work alternate (odd!)Saturdays. So, we loathed those months with 5 Saturdays!!

Raju said...

Aparna, ya I too read about the 2 moon theory (of past). When I read that slow motion collision led to the merging of the two moons, it looked to me more like an 'acquisition'.

Now I know why u favored even numbers to odd ones.

www.inmobiliaria.cn said...

The chap is absolutely just, and there is no question.