Latest TCS Aptitude Question SOLUTION: In a room there are 7 persons. The chance that 2 of them were born on same day of the week

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In a room there are 7 persons.
The chance that 2 of them were born on same day of the week

Asked In TCS (10 years ago)

Unsolved Read Solution (6)

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sravan  (10 years ago)

The answer is 1/7.
The first person can have the birthday in any of the days of the week which gives the probability as 1( ie 7/7).
The second person should have the birthday on the same day as the 1st ones, which decreases the sample spaces to 1day(The birthday of the 1st person), making the probability 1/7. hence total probability = 1*1/7=1/7.
OR
We can the birthday problem's solution, NO 2 PERSONS CAN HAVE THE SAME BIRTHDAY gives
1(1-1/7) = 6/7.
Now the required probability is the chance that 2 of them were born on same day of the week making it 1-6/7=1/7

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ritabrata gautam  (10 years ago)

please correct it 1/7 can never be the answer...its 2160/(7^5)
procedure is
7C2 * 7/7 * 1/7 * (6/7)*(5/7)*(4/7)*(3/7)*(2/7)
^^selecting 2 among those 2nd person and the rest will be left
persons who 2 one can born on exactly with 6,5,4,3,2 days to choose
born on same born on any that day
day day

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veerapuraju pavan ajay  (10 years ago)

total 7 persons so let us take p1,p2,p3,p4,p5,p6,p7
thep can form 7C2 pairs (p1p2,p1p3,p1p4,p1p5,p1p6,p1p7,p2p3,p2p4,p2p5,p2p6,p2p7.........)=21pairs
so each pair can born in any of 7 days so total probability=21*7
let us take from 7 pairs 1 pair of persons as born in same date so 7C1=7
so (7)/(21*7)=1/21
ans =1/21
if wrong correct me pls

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Sandeep negi  (10 years ago)

1-((7c1*6c1)/(7c1*7c1))=1-6/7
=1/7 ans

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ritabrata gautam  (10 years ago)

m4maths messed my description....saying it again...first select 2 persons from 7 who born on same day...then..one of those 2 will will have 7 options while the other will have exactly 1 option(which is chosen by 1)and rest wi be eft with 6,5,4,3,2 option to chose their birth day

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Mahak  (10 years ago)

2/7

Probability of having the two person born on same day is 2 out of 7.

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