Question

Please help: A box contains 5 yellow balls, 3 blue, and 1 red ball. Two balls are drawn at random. Find the probability that:

a
The two balls are yellow

b

The two balls have the same color

c

One of the balls is yellow and the other is red

d

One ball is blue and the other is red

Answer 1

a) 0.2778

b) 0.3611

c) 0.1389

d) 0.0833

Explanation:

We have a total of 5 + 3 + 1 = 9 balls

a) First ball being yellow: we have 5 yellow balls, so P1 = 5/9

Second ball being yellow after one yellow was drawn: we have 4 yellows and 8 balls, so P2 = 4/8 = 1/2

Both yellows: P = P1 * P2 = 5/18 = 0.2778

b) Both blues:

P1 = 3/9 = 1/3

P2 = 2/8 = 1/4

P = P1 * P2 = 1/12 = 0.0833

Both yellows or both blues: 5/18 + 1/12 = 0.2778 + 0.0833 = 0.3611

c) First yellow: P1 = 5/9

Second red: P2 = 1/8

Pa = P1 * P2 = 5/72

or

First red: P3 = 1/9

Second yellow: P4 = 5/8

Pb = P3 * P4 = 5/72

P = Pa + Pb = 10/72 = 5/36 = 0.1389

d) First blue: P1 = 3/9 = 1/3

Second red: P2 = 1/8

Pa = P1 * P2 = 1/24

or

First red: P3 = 1/9

Second blue: P4 = 3/8

Pb = P3 * P4 = 1/24

P = Pa + Pb = 2/24 = 1/12 = 0.0833