A man sells 35 wafers at Rs. 15 each and incurs a loss of Rs. 40.4 on the transaction. If instead he sells the same 35 wafers at Rs. 18 each, what is his profit or loss in rupees, approximately?

Introduction / Context:
This question uses two different selling prices for the same quantity of wafers. The first selling price leads to a known loss in rupees, which allows us to determine the total cost price. With that cost price, we can then compute whether there is a profit or loss at the second selling price and by how much. The arithmetic involves basic linear equations on totals rather than percentages.

Given Data / Assumptions:

• First scenario: 35 wafers are sold at Rs. 15 each.
• Loss in the first scenario is Rs. 40.4.
• Second scenario: the same 35 wafers are sold at Rs. 18 each.
• The cost price per wafer remains the same in both scenarios.
• We must find the profit or loss in rupees in the second scenario, approximately.

Concept / Approach:
First, compute the total selling price in the loss scenario, and then add the loss to obtain the total cost price. From that total cost price, divide by the number of wafers to get the cost price per wafer. Next, compute the total selling price in the second scenario using the higher selling price. Finally, subtract the total cost price from this new selling price to see the net profit or loss. Due to a slightly awkward number 40.4, the final profit will be approximate, so we match the closest integer option.

Step-by-Step Solution:
Total selling price in the first scenario equals 35 * 15 which is 525 rupees.There is a loss of 40.4 rupees, so total cost price equals 525 plus 40.4 which is 565.4 rupees.Cost price per wafer equals 565.4 divided by 35, approximately 16.16 rupees per wafer.In the second scenario, selling price per wafer is 18 rupees.Total selling price in the second scenario equals 35 * 18 which is 630 rupees.Profit in the second scenario equals total selling price minus total cost price equals 630 minus 565.4 which is 64.6 rupees approximately.Among the given options, the closest integer value to 64.6 is 64 rupees, which we take as the approximate profit.

Verification / Alternative check:
We can also check roughly by estimating cost per wafer as about 16 rupees. If cost per wafer were exactly 16 rupees, total cost would be 35 * 16 equals 560 rupees. At 15 rupees each, selling price is 525 rupees, giving a loss of 35 rupees, which is a little less than the given 40.4 rupees. At 18 rupees per wafer, selling price is 630 rupees. With total cost near 565 to 570 rupees, the profit should be slightly above 60 rupees, which is consistent with the 64.6 rupee calculation. Thus, an answer around 64 rupees is reasonable and matches the closest option.

Why Other Options Are Wrong:
Option 52 rupees would imply a much lower difference between the new selling price and the cost price, which contradicts the detailed calculation based on the given loss. Option 72 rupees would require either a lower cost price or higher selling price than we actually have. Option 55 rupees is also not close enough to the derived profit. Only 64 rupees correctly approximates the computed profit of about 64.6 rupees.

Common Pitfalls:
Some learners mistakenly compute the profit in the second scenario relative to the first selling price instead of the cost price, which is incorrect. Others ignore the decimal in 40.4 and assume a neat cost calculation, leading to small discrepancies. In aptitude tests, such slight differences are often rounded, so it is important to look for the option that is closest to the calculated result, not necessarily an exact match when decimals are involved.

Final Answer:
When the wafers are sold at Rs. 18 each, the man makes an approximate profit of Rs. 64.