Aptitude - Probability - Discussion

If we can chose (1,2) and (2,1) (2,3) and (3,2).

Then why we can't chose (1,1) both time. Not only that case we also chose (1,1) as a double event space. Please reply.

1 is prime no or composite no?

Prime number is nothing but a number which is divided by 1 or itself. For example 5 is divided by itself or only 1. So its called a prime number. 6 is not called a prime no because of it can divide by 2, 3. I hope now clear cut.

@Vrushang.

In combination(1, 1) are same, in permutations order is impt ex: (1, 2),(2, 1).

Are same selection in combs we first 1 or 2, 2 or 1 is same comb. But in permutations the arrangement is imp 1, 2 it is different from 2, 1 first 1 is set in the row next second place 2 is set, first 2 is set in the row, next 1 is set in the row.

So I think you are understand.

Hey if you take 5, 6 and 6, 5 as a different pair then why you don't take (1, 1) and (1, 1) as different pairs because it is first time 1 and second time 1.

Finally I found the answer of this question. It is very simple.

When two dice are tossed the total number of possibilities are 36.

Which means 6*6 =36. They are asked to find out the prime number. We know what is prime number, the number is divisible by the same number except 1.

In this concept the possibilities are
(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).

from {(1,1), (1,2)... (6,6)}.

1+1=2, 1+2=3, 1+4=5, 1+6=7 the same way you can get the indivisible numbers expect the same number. So answer is 15/36 which is equal to 5/12 is the correct answer :-).

Why (1, 1) don't consider two times while sets like (1, 2) n (2, 1) is taken two times?

The sample space is a set, so repeated event (1, 1) is taken only once.

Why don't we consider (1, 1) two times. Because it will be the outcome of both the dices.

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.