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?
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 20060215 02:55:57 