# People born on the same day week and month

1. Jan 24, 2007

### hyderman

hello

please can you help explainig that
thanks

How many people are needed to guarantee that at least two were born on the same day of the week and in the same month (perhaps in different years)?

2. Jan 24, 2007

### chanvincent

For the first problem, think of the worst case... you have a group of people, whose born on
different day of the week... what is the maximum size of the group?
Obviouly the answer is seven. If we place one more person into the group, the last person
whose place into the group MUST born on the same day with one of the people whose
already inside the group. Therefore, if we have eight people, at least two of them are born
on the same day. If we have seven, they might be all born on different day...

The second problem is similar to this one...

3. Jan 24, 2007

### cristo

Staff Emeritus
hyderman, In future please show your work when posting in the homework forums. PF rules state that we cannot help unless you attempt the problem first.

4. Jan 30, 2007

### AlephZero

Start by thinking about a simpler question: How many people are needed to guarantee that at least two were born on the same day of the week?

Answering that should give you a clue how to do the full question.

5. Jan 31, 2007

### HallsofIvy

Staff Emeritus
How many times are you going to post this same question? Assuming that you really mean "guarantee", then the obvious answer is one more than the number of days in a year (including Feb 29).

6. Jan 31, 2007

### AlephZero

That's true, but the minimum number of people to guarantee it is much smaller than 367.

But since my previous attempt at helping was ignored by the OP, I'm not going say any more.