Question

Find the missing number.
\[11:17::{\rm{ }}19:?\]
A) 29
B) 27
C) 21
D) 23

Answer 1

Hint:
Here we have to find the given analogy. We will first observe the first two numbers and try to establish the relation between the two. Then using the same relation, we will find the missing number.

Complete step by step solution:
Here we can see that the given numbers 11, 17, 19 are prime numbers. We know that a prime number is defined as a number which has only two factors i.e. one and the number itself.
We can see that there is a gap of one prime number between the prime numbers 11 and 17.
Now, we will first write the few prime numbers from 11.
11, 13, 17, 19, 23, 29, ……
13 is the prime number between 11 and 17. So to find the required number after 19, we will skip one prime number which is 23 here and take into account the next prime number is 29.
As there is a gap of one prime number between 19 and 29, hence, the required mixing number is 29.

Thus, the correct option is option A.

Note:
We have to logically solve this question. First we have to understand the pattern of numbers in which they are arranged and then we will accordingly find the numbers. If we do not know about the prime numbers, then we cannot solve this problem, so to solve that, we must have knowledge about the prime numbers. We can also apply another logic to solve the question.
Here, the difference between 17 and 11 is 6.
So we will add 6 to 19 to find the missing number. Therefore, we get
\[19 + 6 = 25\]
But as the option is not given as 25 we cannot consider it correct but it can be one of the possible answers.