Generating random int with specific condition C#

Question

Consider some special condition, where we want to generate location data with some random speed.

public class Location
{
     public double Lat { get; set; }    
     public double Lng { get; set; }
     public int Speed { get; set; }
     public DateTime Date { get; set; }
}

The speed can be randomly generated using Random.Next() method. Now consider that we are going to have limit of 1 to 200 for speed, and we want that most of the Random.Next(1,200) result be more likely at the rang of 1 to 120 (for example if we have 160 locations, most of the location speeds be at around 1 to 120(about 60% to 80% of the location) and the rest be at about range of 120 to 200)

I know some bad and ugly ways where you can divide your locations randomly into two list of locations and then generate speed separately for those lists, but I'm looking for a better and more efficient way.

Thanks!

Edit : I have to mention that there is a property called Date which is Type of DateTime and defines the time of a locations occurrence. A list of location that is going to be generated will be a path so the speeds being generated should be relative to locations and time to just seem right(for example 2 continues locations can't have 2 unrelative speed like first location : 80KM/h , second location: 140 KM/h in a short time span of 30 seconds) so just the speed, date time and location should seem logically a normal path.

Answer 1

Can't you just use two random numbers? The first to determine which range, and the second to choose a number in the appropriate range?

Random rng = new Random(); // This should only be created once, somewhere.

double proportionInLowerRange = 0.7;

int speed;

if (rng.NextDouble() <= proportionInLowerRange)
    speed = rng.Next(1, 121);
else
    speed = rng.Next(120, 201);

Note: The probabilities are linear across both ranges, so if you wanted a normal distribution this wouldn't work.