ii) A box contains 10 white, 7 black and 3 green balls. 2 balls are drawn at random. Find out the probability that: a) both are white

b) one is white and another is green
c) one is black and another is green

for the first draw 20 balls in the box

for the second there are 19
the rest is obvious.
For example both white
ball one: 10/20 =1/2
ball two: 9/19
so
(1/2)(9/19) = 9/38