Semi-Random Or Engine

Hello Everyone,
I want to be able to pick a random number within a certain range, and I am aware of random.range();

However, I want to be able to have, say, a 75% chance of 1-20, 15% chance of 21-30, 10% chance of 31-35, if that makes sense. Thank you.

Pseudo random number generators have a uniform number distribution. You have to do it in two seperate steps. First use a random float value to define your area and then do another Random.Range to get the actual number

int GetValue()
{
    float n = Random.value;
    if (n < 0.75f)
        return Random.Range(1, 21);
    n -= 0.75f;
    if (n < 15f)
        return Random.Range(21, 31);
    return Random.Range(31, 36);
}