The urn contains 10 white, 4 black and 6 yellow balls of the same size. One ball is taken out of the urn.

The urn contains 10 white, 4 black and 6 yellow balls of the same size. One ball is taken out of the urn. What is the probability that this ball will turn out to be: a) white; b) black; c) yellow; d) white or black?

Let’s count the number of balls – 10 + 4 + 6 = 20 balls.

The outcome is the choice of 1 of any ball, so the number of all outcomes is 20.

a) Favorable outcome – choice of 1 white ball.

1 white ball out of 10 white balls can be chosen in 10 ways.

Then, P = 10/20 = 0.5.

b) Favorable outcome – choice of 1 black ball.

1 black ball out of 4 black balls can be chosen in 4 ways.

Then, P = 4/20 = 0.2.

c) Favorable outcome – choice of 1 yellow ball.

1 yellow ball out of 6 yellow balls can be selected in 6 ways.

Then, P = 6/20 = 0.3.

d) Favorable outcome – choice of 1 black or 1 white ball.

1 black ball out of 4 black balls can be chosen in 4 ways.

1 white ball out of 10 white balls can be chosen in 10 ways.

That is, these balls can be selected in 10 + 4 = 14 ways.

Then, P = 14/20 = 0.7.

Answer: a) P = 0.5; b) P = 0.2; c) P = 0.3; d) P = 0.7.