Aptitude - Probability - Discussion

Discussion Forum : Probability - General Questions (Q.No. 10)
10.
Two dice are tossed. The probability that the total score is a prime number is:
1
6
5
12
1
2
7
9
Answer: Option
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

Discussion:
64 comments Page 2 of 7.

Priyanka said:   6 years ago
Anyone tell me, why not taking (6, 3)?

Harika said:   6 years ago
Hi when would be the sample space be 12 and when would it be 36? I mean if a dice is thrown twice or if two dice are thrown. What would be the difference in the sample space?

Williams said:   6 years ago
In the answer, why didn't they count (1,1) twice as it is possible that the number 1 might come on either of the dices, as they calculated (1,2) & (2,1)

Sirisha said:   7 years ago
1+1=2 here 2 is not a prime number then please explain why (1, 1) used here?

Explain, please.

Durba said:   7 years ago
The sum of (1, 4) (1, 6) is not prime.

Abs Rasel said:   7 years ago
Prime numbers
2={1,1}
3={1,2};{2,1}
5={1,4};{4,1};{2,3};{3,2}
7={1,6};{6,1};{2,5};{5,2};{3,4};{4,3}
11={5,6};{6,5}
Total 15 possible outcomes.

So, Probability is =15/36=5/12.
(3)

Suhail Abdul Rehman Chougule said:   8 years ago
I am sure the answer is 1/6 for this as this event mentioned has something missing.

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) }

E(correct) = { (1,1), (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) }
(1,1) will have a probability 2/12 rather than 1/12 un-like other pairs.

If you note (2,1) occurs and (1,2) also occurs and hence (1,1) due to dice A and additionally (1,1) due to dice B and hence the probability of this event is doubled.

Mahendra said:   8 years ago
Why we enter prime numbers sum as 15? Please explain the step.
(1)

Mirekua said:   8 years ago
Please, from where E={(1,1),(1,2)...} is came? Please explain.

Supriya said:   8 years ago
Can anyone explain the simplest method to find numarator?


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