DeterministicGrouping.cs

public static class DeterministicGrouping
{
    public static bool IsSelected(Guid entropy, ulong numerator, ulong denominator = 100)
    {
        if(numerator > denominator)
            throw new ArgumentOutOfRangeException(nameof(numerator), "The numerator cannot be larger than the denominator.");
        if (numerator <= 0)
            throw new ArgumentOutOfRangeException(nameof(numerator), "The numerator must be a positive non-zero value.");
        if (denominator <= 0)
            throw new ArgumentOutOfRangeException(nameof(denominator), "The denominator must be a positive non-zero value.");

        ulong guidNumericValue = BitConverter.ToUInt32(entropy.ToByteArray().Take(4).ToArray(), 0);

        return guidNumericValue%denominator < numerator;
    }
}