Question

Which statement is true about whether Z and B are independent events?

Z and B are independent events because P(Z∣B) = P(Z).
Z and B are independent events because P(Z∣B) = P(B).
Z and B are not independent events because P(Z∣B) ≠ P(Z).
Z and B are not independent events because P(Z∣B) ≠ P(B).

Answer 1

Z and B are independent events because P(Z∣B) = P(Z).

Explanation:

After a small online search, I've found a table to complete this problem, that we can see below.

For two events Z and B, we have:

P(Z|B) = probability of Z given that B

such that:

P(Z|B) = P(Z∩B)/P(B)

So, two events are independent if the outcome of one does not affect the outcome of the other.

So, if the probability of Z given B is different than P(Z) (the probability of event Z) means that the events are not independent.

So Z and B are independent if the probability of Z given B is equal to the probability of Z.

P(Z|B) = P(Z)

In the table we can see:

P(Z|B) will be equal to the quotient between all the cases of Z given B (126) and the total cases are given B (280)

P(Z|B) = 126/280 = 0.45

Similarly, we can find P(Z):

And P(Z) = 297/660 = 0.45

So we can see that:

P(Z|B) = P(Z)

Thus, B and Z are independent.