Five friends P, Q, X, Y and Z purchased some notebooks. The relevant information is given below :
1. Z purchased 8 notebooks more than X did.
2. P and Q together purchased 21 notebooks.
3. Q purchased 5 notebooks less than P did.
4. X and Y together purchased 28 notebooks.
5. P purchased 5 notebooks more than X did.
If each notebook is priced ₹ 40, then what is the total cost of all the notebooks?

Correct Answer: (A) ₹ 2,600

From conditions 2 and 3: $P + Q = 21$ and $Q = P - 5$, giving $2P - 5 = 21$$\implies$ P = 13 and $Q = 8$. From condition 5: $P = X + 5$$\implies$ X = 13 - 5 = 8. From condition 1: $Z = X + 8 = 8 + 8 = 16$. From condition 4: $X + Y = 28$$\implies$ Y = 28 - 8 = 20. The total number of notebooks is $P + Q + X + Y + Z = 13 + 8 + 8 + 20 + 16 = 65$. At ₹ 40 each, the total cost is $65$$\times$ 40 = $\text{₹ }$ 2,600.