# Aptitude - Odd Man Out and Series - Discussion

Discussion Forum : Odd Man Out and Series - Missing No. (Q.No. 6)
Directions to Solve
Insert the missing number.

6.
11, 13, 17, 19, 23, 29, 31, 37, 41, (....)
43
47
53
51
Explanation:
Numbers are all primes. The next prime is 43.
Discussion:
8 comments Page 1 of 1.

Karan said:   9 years ago
The logic that I used to find answer was:

11-17=6.
23-17=6.
31-23=8.
41-31=10.

Hence difference of numbers at odd place are (6, 6, 8, 10).

And when we repeat this with even place numbers.

19-13=6.
29-19=10.
37-29=8.

This implies that the difference between the missing number and 37 should generate 6 in order to make the set of difference similar to odd place diff set of (6, 6, 8, 10).

-37=6.

=>ans=37+6=43.

Divya said:   10 years ago
Its sequence of prime numbers starting from 11, 13, 17,.....

When we are seeing any sequence then in which way we should judge next number? Means what are the probability that we should check first like even, odd, prime numbers etc ?

11, 13, 17, 19, 23, 29, 31, 37, 41, 43 all are prime numbers, arranged in sequences.
(1)

Absolutely it is right.

I think it is in this order +2, -2, +2, +2, -4, +4, -2, +2. When ever it is increasing by some number decreasing by same number in the next number.
(2)

@Hafiz

13-11=2
17-13=4
19-17=2
23-19=4
29-23=6( Alternative number 2 is not Here)
31-29=2( Alternative number 4 is not here)
37-31=6(Alternative number 2 is not Here)
.....

So The Only Answer is Next Prime is 43.
(1)

I think that

13-11=2
17-13=4
19-17=2
23-17=4
....
41+2=43

the (2,4) (2,4) (2,4 ) is got repeated.
(1)