show that at least 3 of any 25 days chosen must fall in the same month of the year.please halp!
==> In order to figure this out, you have to know that there are 12 months in the year.
Take a calendar. You have to pick 25 days in it.
First 12 days you pick:
You want to avoid bunching them up, so you pick each one
from a different month.
Next 12 days you pick:
You want to avoid bunching them up, so you pick each of these
from a different month too.
So far, you've picked (12 + 12) = 24 numbers, and there are two from each month.
Last day you pick:
You still have to pick one more number to make 25.
What month will you pick it from ?
WHATEVER month you pick it from, you'll have three days from that month.