Seven persons S, E, V, B, A, D and U sit in a row facing north and they all work in a company with different working experience of 15yr, 7yr, 2yr, 23yr, 19yr, 6yr and 12yr. All the information is not necessarily in the same order as given.

The persons with vowel name have experience of even number year and neither sits at the end nor at exactly middle of the row. Three persons sit between S and the one having 23yr experience. One person sits between S and A. The number of persons sits to the right of A is same as the number of persons sits to the left of the one having experience 2.5 times of A. B neither have highest year experience nor sits adjacent to S. The person having least experience sits second to the left of D. U does not have least experience. The neighbors of B have more experience than B.

How many persons sit to the right of the one having 1yr less experience than B?

The correct option is Four.

Let us step-by-step solve the arrangement based on the given clues:

1. Given Data:
Seven persons: S, E, V, B, A, D, U
Experience in years: 15, 7, 2, 23, 19, 6, 12
All face North.

2. Vowels Clue:
The vowels are E, A, U.
They must have even number of experience years. The available even experience values are: 2, 6, 12.
So, E, A, U must have experiences from {2, 6, 12} in some order.
Also, vowels cannot sit at the ends (positions 1 or 7) or in the exact middle (position 4). Thus, vowels can only occupy positions 2, 3, 5, or 6.

3. Experience of A and the condition involving 2.5 times:
Since A is a vowel, its experience is an even number: 2, 6, or 12.
If A's experience is 2, then 2.5 × 2 = 5 (not in the list).
If A's experience is 12, then 2.5 × 12 = 30 (not in the list).
If A's experience is 6, then 2.5 × 6 = 15 (which is present in the given experience values!).
Therefore, A has 6 years of experience, and the person with 15 years of experience corresponds to "2.5 times of A".

4. Position Clue:
"The number of persons sitting to the right of A is the same as the number of persons sitting to the left of the one having 15 years experience."
Since A is a vowel, A cannot sit at position 4. Let's test possible positions for A (2, 3, 5, 6):
If A is at position 3, there are 4 persons to its right, so the person with 15 years experience must have 4 persons to their left (i.e., at position 5).

5. Clues for S and A:
"One person sits between S and A."
If A is at position 3, then S can be at position 1 or position 5.
- If S is at position 5, the person with 15 years experience is also at position 5 (S = 15 yrs).
"Three persons sit between S and the one having 23yr experience."
If S is at position 5, then the person with 23 years experience must be at position 1 (since 5 - 4 = 1).

6. Clue for Least Experience (2 yrs) and D:
"The person having least experience (2 years) sits second to the left of D."
This means: (2 yrs) _ D.
Also, 2 years belongs to one of the vowels (E, A, U). Since A has 6 yrs, 2 yrs must belong to E or U.
Since U does not have the least experience, the person with 2 years of experience must be E.
Thus, E has 2 yrs experience, and E sits second to the left of D: E _ D.
Since E is a vowel, E cannot be at position 1 or 4.
Placing E at position 2 means D is at position 4.
Now the remaining vowel U must be at position 6 (the only remaining available non-end, non-middle spot for vowels!).
Since even experiences are {2, 6, 12}, and E = 2 yrs, A = 6 yrs, U must have 12 years of experience!

7. Completing the Seating Arrangement:
Positions from left to right (1 to 7):
Position 1: S (15 yrs)
Position 2: E (2 yrs)
Position 3: A (6 yrs)
Position 4: D
Position 5: B
Position 6: U (12 yrs)
Position 7: V

Let's check B:
"B neither has highest year experience (23 yrs) nor sits adjacent to S."
Here B is at position 5, which is not adjacent to S (position 1). S has 15 yrs, so S is not 23 yrs either. Position 7 (V) has 23 yrs.
"The neighbors of B have more experience than B."
Neighbors of B (at pos 5) are D (pos 4) and U (pos 6 with 12 yrs).
The remaining experience values for B and D are 7 yrs and 19 yrs.
Since both neighbors of B must have more experience than B, B must have 7 years of experience, and D has 19 years of experience (19 > 7 and 12 > 7 holds true).

8. Final Seating Order and Experience:

1. S - 15 yrs
2. E - 2 yrs
3. A - 6 yrs
4. D - 19 yrs
5. B - 7 yrs
6. U - 12 yrs
7. V - 23 yrs

9. Answering the Question:
B has 7 years of experience.
1 year less experience than B = 7 - 1 = 6 years of experience.
The person having 6 years experience is A (at position 3).
The persons sitting to the right of A are at positions 4, 5, 6, and 7 (D, B, U, V).
Number of persons sitting to the right of A = 4.