A businessman purchased some notebooks for ₹960. If he had bought 8 more notebooks for the same amount, the cost of each notebook would have decreased by ₹4. What was the original number of notebooks purchased?
Solution
✅ Correct Option: 3
Let the original number of notebooks be $n$. Original cost per notebook $=\dfrac{960}{n}$, while the cost per notebook after buying 8 more would be $\dfrac{960}{n+8}$. The decrease in cost is ₹4: $\dfrac{960}{n}-\dfrac{960}{n+8}=4$ Simplifying gives $n(n+8)=1920$. $n^2+8n-1920=0$ The positive root is $n=40$.