Question

There are 7 balls in the bag: 3 blue, 2 red and 2 white. What is the probability that one would pick two balls of the same colour?

Answer 1

Answer:

5/21.

Step-by-step explanation:

Total number of balls = 7.

Prob(Blue on first pick) = 3/7

Prob(Blue on second pick) = 2/6 = 1/3

So Prob( 2 Blue's) = 3/7 * 1/3 = 3/21 = 1/7.

Prob(Red on first pick) = 2/7

Prob(Red on second pick) =  1/6

So Prob( 2 Red's) = 2/7 * 1/6 = 1/21.

Now the Probability of getting 2 white balls is the same as for the red balls

= 1/21.

Finally, the probability of 2 balls of the same colour

= 1/7 + 1/21 + 1/21

= 3/21 + 1/21 + 1/21

= 5/21.

Answer 2

The probability would be 5/21