Question

There are 7 blue counters, 3 green counters and 1 red counter in a bag.

There are no other counters in the bag.
Hubert takes at random 2 counters from the bag.
Work out the probability that both counters are blue.

Answer 1

21/55

Explanation:

7 blue counters, 3 green counters and 1 red counter = 11 counters

1st counter

P(blue)= blue / total = 7/11

Now there are only 10 counters

6 blue counters, 3 green counters and 1 red counter = 10 counters

2nd counter

P(blue)= blue / total = 6/10 = 3/5

P(blue blue) = 7/11 * 3/5 = 21/55