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# Aptitude - Probability - Discussion

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"Everything you can imagine is real."
- Pablo Picasso
10.

Two dice are tossed. The probability that the total score is a prime number is:

[A].
 1 6
[B].
 5 12
[C].
 1 2
[D].
 7 9

Explanation:

Clearly, n(S) = (6 x 6) = 36.

Let E = Event that the sum is a prime number.

 Then E = { (1, 1), (1, 2), (1, 4), (1, 6), (2, 1), (2, 3), (2, 5), (3, 2), (3, 4), (4, 1), (4, 3),       (5, 2), (5, 6), (6, 1), (6, 5) }

n(E) = 15.

 P(E) = n(E) = 15 = 5 . n(S) 36 12

 Ram Reddy said: (Thu, Dec 2, 2010 10:31:38 AM) Please tell me any other method.

 Srinivas said: (Wed, Dec 15, 2010 12:01:55 PM) Hi sir, i am little bit poor in maths, what is the meaning of prime numbers... { (1, 1), (1, 2), (1, 4), (1, 6), (2, 1), (2, 3), (2, 5), (3, 2), (3, 4), (4, 1), (4, 3), (5, 2), (5, 6), (6, 1), (6, 5) } Why do choose those no only ? Why don't you choose (6,6) (2,2)n etc

 Nachiket said: (Thu, Jan 27, 2011 07:12:19 AM) Prime number is a number which is divisible by 1 and that number only.

 Debai said: (Fri, Jan 28, 2011 03:55:49 AM) Hi RAM, if you tossed 2 dice then you get total 6x6 ie 36 possible cases (equallay likely cases) the above mentioned 15points are prime nos (2, 3, 5, 7, 11, 13, 17, 19. ) if you add any one out of 15 get prime no. That's all.

 Sujatha said: (Mon, Jul 25, 2011 03:10:01 PM) Could you please tel me any short methods for Probability?

 Harshini said: (Wed, Sep 14, 2011 02:34:37 PM) Please tel me where to use permutation and where to use combinations. ?

 Prasad said: (Mon, Jan 16, 2012 12:58:43 PM) Hey why we cant take (1,3),(2,2,),(3,1)etc we can take others also na? So please solve this in easy way.

 Anil Singh said: (Wed, Jan 18, 2012 09:03:00 AM) Prime number divisible by 1 and that nimber only but in the case (1,4), (1,6) etc divided by other number like 1,2,3 Please explain.

 Olamikan Adesanmi said: (Fri, Apr 13, 2012 09:09:39 PM) No wot they mean is that the sum (total) is a prime number. So as for (1, 4) , (1, 6) , the sum are 5 and 7 which are prime numbers.

 Rakesh said: (Wed, Jul 25, 2012 11:24:48 PM) Why we not chosen (2, 2) because it also prime number and it divisible by only 2?

 Ramya said: (Sun, Nov 18, 2012 08:46:10 AM) They have left out 6, 3 and 3, 6 then 5, 6 and 6, 5. These also should be included then the total probability becomes 1/2.

 Ravindra said: (Wed, Nov 28, 2012 12:22:28 PM) @Harshini. Permutations are used for arrangement where as combinations are used for selection. Ex: Arrange the name xyz then per is used. Where as, Select one among this xyz comb is used.

 Siva said: (Sat, Feb 16, 2013 07:58:36 PM) Prime number means the we gets only one time. i.e., 1*2=2 only once we get 2. But for 4 1*4=4, 2*2=4 now we get 4 for 2 times in-terms of multiplication.

 Ganesh Sang said: (Fri, Feb 22, 2013 02:00:52 PM) Please in every example we need to find samples or experiment samples or there is any shortcut for easily getting number of prime number or sum of two numbers as a prime ?

 Suvendu said: (Mon, Feb 25, 2013 10:33:59 PM) As the question says sum should be a prime number. So sum must be 2, 3, 5, 7, 11, So probability should be (1, 1) (1, 2) (2, 1) (1, 4) (4, 1) (3, 4) (4, 3) (5, 6) (6, 5). So probability= (9/36) =1/4.

 Akshay said: (Fri, Apr 26, 2013 12:32:21 PM) Why don't we consider (1, 1) two times. Because it will be the outcome of both the dices.