Q - In a room there are 7 persons.The chances that the two of them born on the same day of week.
a) 1080/7^5 b) 2160/7^5 c) 540/7^4 d) None of these
Any hint would be greatly appreciated.
Thanks,
Ashish
Hello, Ashish!
I got "None of these" until I read the problem again . . .In a room there are 7 persons.
Find the probability that two of them are born on the same day of week.
. .
I believe the problem means "exactly two have the same weekday of birth".
There are: . ways to pick the two people.
. . Call them and
can have any day for his birthday:
. . must have the same day: .
. . . . must have one of the remaining six days: .
. . . . . . must have one of the remaining five days: .
. . . . . . . . must have one of the remaining four days: .
. . . . . . . . . . must have one of the remaining three days: .
. . . . . . . . . . . . . must have one of the remaining two days: .
Therefore, the probability is: .
. . which simplifies to: . . . . answer (c)