What is the probability that the sum of any two different single digit...
Solution:
Prime numbers between 1 to 9 are 2, 3, 5 and 7. Let's take all possible pairs of natural numbers whose sum is less than or equal to 9.
(1,2), (1,3), (1,4), (1,5), (1,6), (1,7), (1,8), (1,9)
(2,3), (2,4), (2,5), (2,6), (2,7), (2,8)
(3,4), (3,5), (3,6), (3,7)
(4,5), (4,6), (4,7)
(5,6), (5,7)
(6,7)
Out of these pairs, we can see that only 8 pairs have a sum that is a prime number.
(1,2), (1,4), (1,6), (2,3), (2,5), (3,4), (3,8), (4,3)
Therefore, the probability that the sum of any two different single digit natural numbers is a prime number is 8/36 or 7/18.
Answer: Option B. 7/18.