Wednesday puzzle

[Sausage Surprise]

Is the answer 7?

[MyUserName]

3 men meet by chance. What are the probabilities that:

(1) None of them share a birthday
(2) 2 of them share a birthday
(3) All 3 share a birthday

Show yer logic.

I am rubbish at this sort of thing but I will have a go:

None share a birthday:

364/365 * 363/365

Logic being that someone has to have a birthday which is not the same as the first. Hence only 364 days are available, the other guy cannot have the same birthday as the other two hence only 363 days are available.

2 people out of 3 share a birthday:

1/365 + 1/365

Either the first guy has the same day as the first or the other guy has the. This could happen 3 different times as there are 3 ways of pairing the 3 together:

3 x (1/365 + 1/365) = 6/365


All 3 share a birthday:

1/365 * 1/365

As the first person's birthday does not matter but the other two must be on the same day


Is this vaguely correct?

[DimPrawn]

Birthdays are not uniformly distributed throughout the year, so whatever childish maths you are going to come out with shows your stupidity for solving real world problems.

Hence why your biggest challenge this week will be cleaning the oven for your wife.

HTH BIDI

[EternalOptimist]

zero
100%
100%

[sasguru]

A clue to the puzzle

These rules are all you need:

P(A and B and ...) = P(A) x P(B)... (if A and B and ... are independent)
P(A or B or ...) = P(A) + P(B) ... (if A and B and ... are mutually exclusive)

[sasguru]

I am rubbish at this sort of thing but I will have a go:

None share a birthday:

364/365 * 363/365

Logic being that someone has to have a birthday which is not the same as the first. Hence only 364 days are available, the other guy cannot have the same birthday as the other two hence only 363 days are available.

2 people out of 3 share a birthday:

1/365 + 1/365

Either the first guy has the same day as the first or the other guy has the. This could happen 3 different times as there are 3 ways of pairing the 3 together:

3 x (1/365 + 1/365) = 6/365


All 3 share a birthday:

1/365 * 1/365

As the first person's birthday does not matter but the other two must be on the same day


Is this vaguely correct?

Along the right lines .....
In fact no (3) is spot on. As is no (1). Apologies.
2 is quite hard but if you have 1 and 3 you should be able to do it

[sasguru]

Birthdays are not uniformly distributed throughout the year, so whatever childish maths you are going to come out with shows your stupidity for solving real world problems.

Hence why your biggest challenge this week will be cleaning the oven for your wife.

HTH BIDI

You really are thick as 20 planks put together aren't you?

BTW we have a cleaner.

[d000hg]

I can hear the noise of frantic googling

Presumably that's where you got the question from in the first place.

Some of us have non-imaginary (if you'll excuse the maths pun) work to do...

[sasguru]

Presumably that's where you got the question from in the first place.

Some of us have non-imaginary (if you'll excuse the maths pun) work to do...

Nope. It was actually a question on the PPE exam for Hilary College, Oxford, 1965.
Was looking at my old Stats papers.

[MarillionFan]

Nope. It was actually a question on the PPE exam for Hilary College, Oxford, 1965.
Was looking at my old Stats papers.

1965(!) How fookin old are you!!!!!!!!