Reynolds Superink pens are bought at the rate of 8 for ₹ 100. To make a profit of 60 per cent, these must be sold at

### Concept & Formula To find the selling rate for a specific profit margin, first determine the desired Selling Price (SP) for a single unit. $$SP = CP \times \left(1 + \frac{\text{Profit } \%}{100}\right)$$ ### Step-by-Step Solution * **Given:** CP of 8 pens = ₹ 100. Desired profit = 60%. * **Calculation:** 1. CP of 1 pen = $\frac{100}{8} = \text{₹ } 12.5$ 2. Desired SP of 1 pen = $12.5 \times \left( 1 + \frac{60}{100} \right) = 12.5 \times 1.6$ 3. $SP = \text{₹ } 20$ 4. Now, evaluate the given options to see which matches an SP of ₹ 20 per pen. 5. Option (a): 5 for ₹ 100 $\rightarrow$ SP = $\frac{100}{5} = \text{₹ } 20$. This matches. ### Exam Strategy & Shortcut You can apply the multiplier directly to the total cost of the batch. If CP of 8 pens is ₹ 100, the SP of those 8 pens for a 60% profit must be $100 \times 1.60 = \text{₹ } 160$. So, SP rate is 8 pens for ₹ 160. Simplify this ratio: 8 for 160 is the same as 1 for 20, which is the same as 5 for 100. ### Common Pitfall Misinterpreting the options and failing to reduce them to a per-unit price for comparison. Always normalize to the price of a single item to cross-check. ### Final Answer Therefore, the correct answer is **5 for ₹ 100**.