Eight persons — A, B, C, D, E, F, G and H — were born on two different dates i.e. 5th and 12th of four different months viz. January, March, April and June of the same year. No two persons were born on the same day.

C was born on an odd date in the month having even number of days. Three persons were born between C and F. As many persons were born before F as after B. Four persons were born between D and B. G was born immediately before D. A was born on an odd date. E was born before H.

How many persons were born between A and D?

The correct answer is Three.

Let us analyze the given information step-by-step to determine the chronological birth order of the eight persons: A, B, C, D, E, F, G, and H.
First, we list the eight possible birth dates in chronological order:
1. January 5 (31 days, Odd date)
2. January 12 (31 days, Even date)
3. March 5 (31 days, Odd date)
4. March 12 (31 days, Even date)
5. April 5 (30 days, Odd date)
6. April 12 (30 days, Even date)
7. June 5 (30 days, Odd date)
8. June 12 (30 days, Even date)

Step 1: Locate C and F
According to the clues:
- "C was born on an odd date in the month having even number of days." The months with an even number of days (30 days) are April and June, and the odd date is the 5th. Thus, C must be born on either April 5 (position 5) or June 5 (position 7).
- "Three persons were born between C and F."
Let's check the two possibilities for C:
• Case A: If C is born on April 5 (position 5), F must be born on January 5 (position 1) to have exactly three persons between them (positions 2, 3, and 4).
• Case B: If C is born on June 5 (position 7), F must be born on March 5 (position 3) to have exactly three persons between them (positions 4, 5, and 6).

Step 2: Locate B and D
- "As many persons were born before F as after B."
• In Case A (F at position 1): There are 0 persons born before F. Therefore, there must be 0 persons born after B, placing B at June 12 (position 8).
• In Case B (F at position 3): There are 2 persons born before F. Therefore, there must be 2 persons born after B, placing B at April 12 (position 6).
- "Four persons were born between D and B."
• In Case A (B at position 8): The four positions between B and D are 7, 6, 5, and 4. This means D must be at March 5 (position 3).
• In Case B (B at position 6): The four positions between B and D are 5, 4, 3, and 2. This means D must be at January 5 (position 1).

Step 3: Locate G and eliminate the invalid case
- "G was born immediately before D."
• In Case A (D at position 3): G must be born at January 12 (position 2). This is a valid position.
• In Case B (D at position 1): There is no position before position 1. Therefore, Case B is eliminated.

Step 4: Place the remaining persons (A, E, and H)
Using the valid arrangement from Case A:
1. January 5: F
2. January 12: G
3. March 5: D
4. March 12: (Vacant)
5. April 5: C
6. April 12: (Vacant)
7. June 5: (Vacant)
8. June 12: B

Now we apply the remaining clues:
- "A was born on an odd date." The only vacant odd date is June 5 (position 7). Thus, A is born on June 5.
- "E was born before H." The remaining vacant positions are 4 (March 12) and 6 (April 12). Since E is born before H, E must be at position 4 and H must be at position 6.

Final Arrangement:
1. January 5: F
2. January 12: G
3. March 5: D
4. March 12: E
5. April 5: C
6. April 12: H
7. June 5: A
8. June 12: B

Conclusion:
We need to find the number of persons born between A (June 5, position 7) and D (March 5, position 3).
The persons born between them are E, C, and H (at positions 4, 5, and 6 respectively).
Thus, there are exactly Three persons born between A and D.