IndiaBIX

Aptitude - Probability - Discussion

Discussion Forum : Probability - General Questions (Q.No. 10)
Probability
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 7 of 7.
Aniket said:   1 decade ago
The total no of unique combinations on throw of 2 dice is 36:

i.e. {(1,1),(1,2),(2,1),(1,3),(3,1),(2,2),(1,4),(4,1),(2,3),(3,2),(1,5),(5,1),(2,4),(4,2),(3,3),(1,6),(6,1),(2,5),(5,2),(3,4),(4,3),(2,6),(6,2),(3,5),(5,3),(4,4),(3,6),(6,3),(4,5),(5,4),(4,6),(6,4),(5,5),(5,6),(6,5),(6,6)}.

Out of these pairs, how many give us a prime number sum = 15.

i.e. {(1,1),(1,2),(2,1),(1,4),(4,1),(2,3),(3,2),(1,6),(6,1),(2,5),(5,2),(3,4),(4,3),(5,6),(6,5)}.

So, probability = 15/36 = 5/12.
Saranya said:   1 decade ago
Why 4 kings are taken?
Sasikala said:   1 decade ago
Could any one of you explain me in simplistic processes?
Indrajit said:   10 years ago
Hey @Prasad,

Here is the clarification of your doubt. You have to choose those number of pairs whose sum is a prime number. If you choose (1, 3), (2, 2) & (3, 1) then their sum will be 4 which is not a prime number.

Thanks!
Post your comments here:

Your comments will be displayed after verification.

Quick links
Quantitative Aptitude
Verbal (English)
Reasoning
Programming
Interview
Placement Papers