Prove If 25 days are randomly chosen from any one calendar y

Prove: If 25 days are randomly chosen from any one calendar year, then at least 3 of the chosen days will be from the same month.

Solution

we know that 12 months have in a year. then we can be select distinct 12 days from 12 months again similary salect 12 days. we selected 12 +12 = 24 days where we chosen 2 days from 1 month. hence we select 25 day will be choose from any 1 months from 12 months and this month have days = 2+1=3 days

hence proved