Probability Question 412

Question: Out of 30 consecutive numbers, 2 are chosen at random. The probability that their sum is odd, is

[Kurukshetra CEE 2002]

Options:

A) $ \frac{14}{29} $

B) $ \frac{16}{29} $

C) $ \frac{15}{29} $

D) $ \frac{10}{29} $

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Answer:

Correct Answer: C

Solution:

  •                 The total number of ways in which 2 integers can be chosen from the given 30 integers is  $ ^{30}C_2. $  The sum of the selected numbers is odd if exactly one of them is even and one is odd.                    \ Favourable number of outcomes =  $ ^{15}C_1{{.}^{15}}C_1 $                      
    

$ \therefore $ Required probability $ =\frac{^{15}C_1.{{,}^{15}}C_1}{^{30}C_2}=\frac{15}{29} $ .