Q. Five friends P, Q, X, Y and Z purchased some notebooks. The relevant information is given below:

Explanation : 

Five friends p q x y z purchased some notebooks

Now, let’s analyze the given information:

1. Z purchased 8 notebooks more than X did.
Z = X + 8
2. P and Q together purchased 21 notebooks.
P + Q = 21
3. Q purchased 5 notebooks less than P did.
Q = P – 5
4. X and Y together purchased 28 notebooks.
X + Y = 28
5. P purchased 5 notebooks more than X did.
P = X + 5

Now we have a system of 5 linear equations with 5 unknowns. Let’s solve the system step by step:
Step 1: Substitute equation (3) into equation (2):
P + (P – 5) = 21
2P – 5 = 21
2P = 26
P = 13
Step 2: Substitute the value of P from step 1 into equation (5):
13 = X + 5
X = 8
Step 3: Substitute the value of X from step 2 into equation (1):
Z = 8 + 8
Z = 16
Step 4: Substitute the value of X from step 2 into equation (4):
8 + Y = 28
Y = 20
Step 5: Substitute the value of P from step 1 into equation (3):
Q = 13 – 5
Q = 8

Now we have the number of notebooks purchased by each friend:
P = 13, Q = 8, X = 8, Y = 20, Z = 16

The total number of notebooks is:
Total notebooks = P + Q + X + Y + Z = 13 + 8 + 8 + 20 + 16 = 65

Since each notebook is priced at 40, the total cost of all notebooks is:
Total cost = Total notebooks * Price per notebook = 65 * 40 = 2600

The total cost of all the notebooks is 2600.