In a throw of three dice, what is the probability of getting one prime number, one composite number and one number which is neither prime nor composite?

An integer is chosen at random from the first 50 integers. What is the probability that the integer is neither divisible by 5 nor 9?

Out of 50 consecutive natural numbers, two integers are chosen at random. What is the probability that their sum is odd?

The standard deviation of 100 observations is 10. If 20 is added to each observation, then what will be the new standard deviation?