Student: There are 20 balls in a box: 11 balls are green, 6 are blue and 3 are white. Then 1 green and 1 blue balls are taken from the box and put away. What is the probability that a green ball is selected at random from the box?
Options:
(A) 1/13
(B) 10/18
(C) 3/13
(D) 5/13
(E) 6/13.
Another student: Let's say, hmmm...
If 1 green and 1 blue ball are taken from the box, then there are 10 green, 5 blue and 3 white balls, a total of 18 balls. If one ball is selected at random, the probability that it is green is given by 10 / 18 Final answer: (B).