Same Birthday Same year?

[avrilwood]

What are the odds on two English people who are complete strangers, meeting abroad on holiday and having the same birthday and also the same year of birth?

Also taking into account that one of them had been there six days, had not spoken to anyone else since arriving abroad. The other had just arrived and had not spoken to anyone else either and were not staying in the same hotel.

[Bottom]

Are you both the same sex?

[Hamish]

one in 365 timesed by how old you are. However this is based on not holidaying in an area where there is an age bias, ie 18-30, where the odds will be much lower. Also brith rates vary from month to month, therefore if you were born in a very common month, it would be more liekly that you would meet someone with the same birthday. The cal above is a very rough approx. Interestingly though it is the coincidence that seems suprising. If however you took all the information about your life and then found a brit and did the same you would proabbly find at least one 'amazing coincedence'.

The real supprise would be if you went on said holidy with the object of meeting someone with the same birthday/year, rather than just going on holiday and meeting someone who has something about them that tallies with your life.

[jake-the-peg]

Ah no Hamish.

This is only the odds if you are only meeting one person. You actually meet lots of people where this is not the case and you never think how unlikley this is.

Therefore it's actually a lot more likely than you'd think.

[JudgeJ]

In any group of twenty-three people taken at random, there is a more than 50% chance that any two of them will share the same birthday (just the date, not the year). This probability increases to 90% when the group size increases to 41.

The possibility of two people sharing the same birthday (including the year) depends on the age variation in the group. (A class of schoolchildren, for example, will usually all be born within twelve months of each other). In covering an age range of 50 years you are looking for coincident birthdays among about 18,260 dates (365 x 50 plus a few for leap years). You need a random group of about 160 people before the chances are greater than 50% that two of them will share a birthday including the year.

None of this is the same as looking at the odds against any two people sharing the same birthday. The odds against any two people sharing a birthday (regardless of the year) are 1 in 365 (ignoring the chance that one of them may have been born on February 29). To calculate the odds against an exact match the age range of the group, and the proportion of people in each year of the range must be factored in. In a simple case covering five years, with equal numbers in each of the years the odds against a coincidence are 1 in 365 multiplied by 5 (1 in 1825 – ignoring leap years).

[avrilwood]

yes we are both the same sex