Directions (81-85): Study the following information carefully and answer the questions given below:

Eight persons buy different things one after other. Two persons buy between M and L who buys immediately before Q. O buys two persons before Q. As many persons buy between O and Q as between L and K. K buys before O. Two persons buy between K and P. J buys before N and after P.

How many persons buy between M and N?

To find the number of persons who buy between M and N, let us reconstruct the step-by-step buying order of the eight persons based on the given clues.

Let the positions of the 8 persons from first (1st) to last (8th) be represented by positions 1 to 8.

Clue 1: L buys immediately before Q. This means we have the consecutive pair: L, Q.
Clue 2: O buys two persons before Q. "Two persons before Q" means there is exactly 1 person between O and Q (i.e., O _ Q). Since L is immediately before Q, O must be immediately before L. Thus, the order is: O, L, Q.
Clue 3: As many persons buy between O and Q as between L and K. There is exactly 1 person between O and Q (which is L). Therefore, there must be exactly 1 person between L and K. This gives two possibilities for K: either K is before L (K _ L) or K is after L (L _ K).
Clue 4: K buys before O. Since K must buy before O, and our sequence is O, L, Q, K cannot be placed after L. Thus, K must be placed before L. Since there is exactly one person between L and K, and O is immediately before L, K must be immediately before O. So the sequence becomes: K, O, L, Q.
Clue 5: Two persons buy between K and P. Since K, O, L, Q are consecutive, let's look at the positions. K is at the first position of this block. Two persons between K and P means P can be either before K (P _ _ K) or after K (K _ _ P). Since K, O, L, Q has O and L after K, P must be placed after L. Specifically, K (1st), O (2nd), L (3rd), P (4th), Q (5th) is not possible because Q is immediately after L. So the order must be: K, O, L, Q, with P placed 3 positions after K (so two persons, O and L, are between K and P). This means P is immediately after L? No, let's count: K (1), O (2), L (3), Q (4). The two persons between K and P must be O and L. Thus, P must be in position 4, which is currently occupied by Q. This is a contradiction. Let's re-evaluate: "Two persons buy between K and P" means: K _ _ P or P _ _ K. If K is followed by O, L, Q, then the sequence is K, O, L, Q. The two persons between K and P can be O and L, making P occupy the position of Q (which is impossible), or they can be L and Q, making P occupy the position after Q. If P is after Q: K (1), O (2), L (3), Q (4), _ (5), P (6). Here, the persons between K and P are O, L, Q (which is 3 persons, not 2). For exactly 2 persons to be between K and P, P must be: K, O, L, P, Q (not possible since L is immediately before Q) or P, _, _, K, O, L, Q. Let's write down the block: P _ _ K O L Q. This block has 1 (P) + 2 (spaces) + 4 (K, O, L, Q) = 7 persons.
Let us check this block: P, space1, space2, K, O, L, Q.
- The number of persons between K and P is indeed two (space1 and space2).
- K buys before O.
- O is two persons before Q (O, L, Q).
- L is immediately before Q.
- The number of persons between O and Q (which is 1, L) is equal to the number of persons between L and K (which is 1, O). This perfectly matches.
So, the sequence of 7 persons is: P, [space1], [space2], K, O, L, Q. Since there are 8 persons in total, this block of 7 can occupy positions 1 to 7 or positions 2 to 8.
Clue 6: Two persons buy between M and L. In our sequence, L is near the end: P, [space1], [space2], K, O, L, Q. L is the 6th member of this 7-member group. Two persons between M and L means M can be 3 positions before L or 3 positions after L.
If M is 3 positions before L, M must be in [space2] (since the order is [space2], K, O, L). So we get: P, [space1], M, K, O, L, Q. This fits the 7-member group.
Clue 7: J buys before N and after P. Since P is at the very beginning of our 7-member group, J and N must be placed after P.
Let's look at the remaining vacant positions. In the 7-member sequence: P, [space1], M, K, O, L, Q, the only vacant position within the block is [space1]. If we place the 8th person, the positions can be:
Case A: The block is in positions 1 to 7. The 8th position is position 8. The sequence is: P (1), [space1] (2), M (3), K (4), O (5), L (6), Q (7), [space2] (8). The two empty spaces to be filled by J and N are position 2 and position 8. Since J buys before N, J must be at position 2 and N must be at position 8. Let's check: J is before N and after P. Since P is at 1, J at 2 is indeed after P. This is a valid arrangement:
1. P
2. J
3. M
4. K
5. O
6. L
7. Q
8. N

Let's verify Case B: The block is in positions 2 to 8. The 1st position is empty. The sequence is: [space] (1), P (2), [space1] (3), M (4), K (5), O (6), L (7), Q (8). Here, J must buy after P. Since P is at position 2, the empty spaces after P are position 3. But we have only one empty space after P (position 3), and we need to place both J and N after P such that J is before N. We cannot place both in one space. The other empty space is position 1, which is before P, so we cannot place J or N there because both must be after P. Thus, Case B is invalid.

Therefore, the unique final sequence of the eight persons buying things from 1st to 8th is:
1. P
2. J
3. M
4. K
5. O
6. L
7. Q
8. N

The question asks: How many persons buy between M and N?
M is at position 3 and N is at position 8.
The persons between M and N are at positions 4, 5, 6, and 7, which are K, O, L, and Q respectively.
Counting them, we find there are exactly 4 persons (K, O, L, Q) between M and N.

Thus, the correct option is Four.