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Friday the 13th (Posted on 2004-08-13) Difficulty: 4 of 5
Which day of the week (Sunday, Monday, etc.) is the probability largest to fall on the 13th of a random month, in a random year?

Or is this probability the same for each day of the week?

See The Solution Submitted by SilverKnight    
Rating: 3.5000 (4 votes)

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Solution belated | Comment 12 of 13 |

 

The first day of each month position on a normal year and leap year based on sunday as first day are as follows. let monday rep 1, tuesday rep 2 and so on and sunday rep 0

0 3 3 6 1 4 6 2 5 0 3 5 and

0 3 4 0 2 5 0 3 6 1 4 6 respectively

for normal years & leap years

day on which 13 falls would be as follows

4 0 0 3 5 1 3 5 2 4 0 2 and

4 0 1 4 6 2 4 6 3 5 1 3 respectively 

varying first day from 0 to 6 we get the probability of getting any number from 0 to 6 for both leap years and normal years is the same. Hence there is equal chance of getting any day for 13th.

 

 


  Posted by salil on 2006-02-15 02:55:57
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