Two glass balls, two ivory balls, two cork balls, two cast iron balls, two lead balls collide.

Two balls are selected from two black and two red balls. The probability that the two balls will have no black balls is

Two balls are selected from two black and two red balls. The probability that the two balls will have no black balls is

Prove that in a two dimensional elastic collision of a moving ball with another stationary identical ball, the two balls move perpendicular to each other after collision?

A bag contains b blue balls and r red balls. If two balls are drawn at random, the probability drawing two red balls is five times the probability of drawing two blue balls. Furthermore, the probability of drawing one ball of each color is six times the probability of drawing two blue balls. Then

A bag contains b blue balls and r red balls. If two balls are drawn at random, the probability drawing two red balls is five times the probability of drawing two blue balls. Furthermore, the probability of drawing one ball of each color is six times the probability of drawing two blue balls. Then

from a bag containing 4 red and 2 black balls, two balls are drawn. the probability of getting two black balls is:

A bag contains 9 yellow balls, 3 white balls and 4 red balls. In how many ways can two balls be drawn from the bag?