Question

5. [Statistical independence] Consider a month consisting of exactly 28 days, split into four weeks of seven days each, such that the first of the month is a Monday. One of the 28 days will be selected uniformly at random (so that each day has probability 1/28 of being selected). Event A is that the selected day is a Monday or Wednesday. Event B is that the selected day falls either in the first or third weeks of the month. Are A and B independent or not? Show your work.

Answer 1

They are independent events

Explanation:

For independent events;

Pr(A & B) = Pr(A) × Pr(B)

Given that:

A = day is Monday or Wednesday

Since we have four weeks and each week will have one Monday and Wednesday each,

Pr(A) = (8/28)

B = day falls in the first or third week

Since, first and the third week has a total of 14 days,

Pr(B) = 14/28

Therefore;

Pr(A) × Pr(B) = 8/28 * 14/28

Pr(A) × Pr(B) = 1/7

Now, A and B = day is either Monday or Wednesday, and it is in the first or third week

There are four such days, Thus Pr(A and B) = 4/28 = 1/7

Since, Pr(A and B) = Pr(A) * Pr(B),

A and B are independent events