internal class Program
{
static void Main(string[] args)
{
int rangeStart = 50;
int rangeEnd = 150;
int randMin = 10;
int randMax = 26;
int counter = 0;
int baseNumber;
int currentNumber;

Random random = new Random();
baseNumber = random.Next(randMin, randMax);
currentNumber = baseNumber;

while (currentNumber <= rangeEnd)
{
if (currentNumber >= rangeStart)
{
counter++;
}

currentNumber += baseNumber;
}

Console.WriteLine($"Количество чисел от {rangeStart} до {rangeEnd} (включая эти числа)," +
$" которые кратны {baseNumber} ровняется - {counter}");
Console.ReadKey();
}
}