Q. In a room there are 7 persons. The chance that two of them were born on the same day of the week is

Opyion
A)109=80/7^5
B)2160/7^5
C)540/7^4
D)None of these

• first select two person from 7 in 7C2 ways.
  select a day which they have to be born in 7C1 ways.
  for the remanning 5 people select 5days out of 6days of week and no. of arrangment of these 5 people in 5 days = (7C2*7C1*6C5*5!)ways.
  also,7 people born on 7 days whould be 7^7
  hence
  (7C2*7C1*6C5*5!)/(7^7) =2160/7^5
  
  
  
• 10 years agoHelpfull: Yes(0) No(1)