Answer:
P(Y = 0) = 0.09
P(Y = 1) = 0.4
P(Y = 2) = 0.32
P(Y = 3) = 0.19
Explanation:
Let the events be:
Wednesday
Thursday
Friday
Saturday
Their corresponding probabilities are

Since
= number of days beyond Wednesday that it takes for both magazines to arrive(so possible
values are 0, 1, 2 or 3)
The possible number of outcomes are therefore

The values associated for each of the outcomes are as follows:

The probability mass function of
is,
![P(Y = 0) = 0.3(0.3) = 0.09\\P(Y = 1) = P[(W, T) or (T, W) or (T, T)]\\= [0.3(0.4) + 0.3(0.4) + 0.4(0.4)]\\= 0.4\\\\P(Y = 2) = P[(W, F) or (T, F) or (F, W) or (F, T) or (F, F)]\\= [0.3(0.2) + 0.4(0.2) + 0.2(0.3) + 0.2(0.4) + 0.2(0.2)]\\= 0.32\\\\P(Y = 3) = P[(W, S) or (T, S) or (F, S) or (S, W) or (S, T) or (S, F) or (S, S)]\\= [0.3(0.1) + 0.4(0.1) + 0.2(0.1) + 0.1(0.3) 0.1(0.4) + 0.1(0.2) + 0.1(0.1)]\\= 0.19](https://img.qammunity.org/2021/formulas/mathematics/college/ak95tbqlb4cdx6f7z0qo0y92cpkhfl6cxd.png)