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In Heroes of Might and Magic I, the base damage is generated separately for each unit in the squad.
Example 1: Let's say a squad consists of 3 dragons. The base damage is the sum of 3 numbers from the range [25-50]. For example, the base damage could be 25 + 25 + 25 = 75, or 31 + 47 + 28 = 106, or 50 + 50 + 50 = 150, etc. Obviously, the base damage of 3 dragons ranges from 3*25 = 75 to 3*50 = 150. An inexperienced player might think that all damages in the range [75-150] are equally likely, but this is not the case.
Example 2: Three gnomes ([2-4]) deal base damage from the range [3*2-3*4] = [6-12], i.e., the base damage of three gnomes can be 6, 7, 8, 9, 10, 11, or 12. Let's consider all the cases:
1 2 3
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2 2 2 = 6
2 2 3 = 7
2 2 4 = 8
2 3 2 = 7
2 3 3 = 8
2 3 4 = 9
2 4 2 = 8
2 4 3 = 9
2 4 4 = 10
3 2 2 = 7
3 2 3 = 8
3 2 4 = 9
3 3 2 = 8
3 3 3 = 9
3 3 4 = 10
3 4 2 = 9
3 4 3 = 10
3 4 4 = 11
4 2 2 = 8
4 2 3 = 9
4 2 4 = 10
4 3 2 = 9
4 3 3 = 10
4 3 4 = 11
4 4 2 = 10
4 4 3 = 11
4 4 4 = 12
The total number of possible combinations is n^k, where n is the number of units in the squad, and k is the length of the range for one unit (the number of possible damage values). In our case, n = 3, k = 4 - 2 + 1 = 3. Therefore, n^k = 3^3 = 27. As you can see, the damage of 6 can be obtained in only one way (when all three gnomes generate a damage of 2), the damage of 7 can be obtained in 3 ways, and so on.
6 - 1 way (1 out of 27, probability of 1/27)
7 - 3 ways (3/27)
8 - 6 ways (6/27)
9 - 7 ways (7/27)
10 - 6 ways (6/27)
11 - 3 ways (3/27)
12 - 1 way (1/27)
Thus, 3 gnomes are most likely to deal 9 damage (probability 7/27 = 25.9%). The probability of dealing 6 or 12 damage is only 1/27 = 3.7%. In the additive theory of numbers, the above decompositions (e.g., 10 = 2 + 4 + 4) are called compositions with M parts (in our case, M = 3), where each part does not exceed a given number N. The number of such compositions is denoted by c(N, M, n). There is a formula for c(N, M, n). I will not provide it here (it is not simple).
Therefore, the probability of a specific damage value = c(N, M, n)/n^k. The probability of damage values at the ends of the range decreases sharply as the number of units in the squad increases. Damage values from the center of the range are more likely. The theory is in excellent agreement with practice (the probability distribution of damage values has been verified by testers).
Why is this important?
a) To avoid being surprised if your squad does not deal maximum (or close to maximum) damage;
b) To be surprised if this happens to your opponent;
Knowing the probabilities of damage values will also help you assess the effectiveness of your squads (e.g., which one is better).
I would also like to note that the above reasoning is also valid for Heroes of Might and Magic III (when the number of units in the squad does not exceed 10; the qualitative part of the post is also valid for other cases).