The marked price of a shirt is Rs. 100 and the marked price of a pair of trousers is Rs. 300.\nA 10% discount is given on the shirt and a 20% discount is given on each pair of trousers.\nIf Pritam buys 1 shirt and 3 pairs of trousers, what is the overall effective discount percentage on his total purchase?

Introduction / Context:
This question involves different discount rates applied to different items in a single purchase. The goal is to determine the effective discount percentage on the total bill for Pritam. This scenario is very common in real shopping cases where different products have different offers and is frequently tested in percentage and profit and loss sections of aptitude exams.

Given Data / Assumptions:

• Marked price of one shirt = Rs. 100.
• Marked price of one pair of trousers = Rs. 300.
• Discount on the shirt = 10% of its marked price.
• Discount on each pair of trousers = 20% of its marked price.
• Pritam buys 1 shirt and 3 pairs of trousers.

Concept / Approach:
The effective discount percentage is based on the total marked price for all items and the total amount actually paid after item wise discounts. We first compute the total marked price. Then we calculate the discounted price for the shirt and the trousers separately, sum these to get the actual payment, and finally compute the overall discount percentage using the formula effective discount = (total marked price - total paid) / total marked price * 100.

Step-by-Step Solution:
Step 1: Compute the total marked price.Marked price for 1 shirt = 1 * 100 = Rs. 100.Marked price for 3 trousers = 3 * 300 = Rs. 900.Total marked price = 100 + 900 = Rs. 1,000.Step 2: Compute actual payment for the shirt.Discount on shirt = 10% of 100 = 10, so shirt price after discount = 100 - 10 = Rs. 90.Step 3: Compute actual payment for the trousers.Discount per trouser = 20% of 300 = 60, so price after discount for one trouser = 300 - 60 = 240.Step 4: Total for 3 trousers after discount = 3 * 240 = Rs. 720.Step 5: Total amount actually paid by Pritam = 90 + 720 = Rs. 810.Step 6: Total discount amount = total marked price - total paid = 1,000 - 810 = Rs. 190.Step 7: Effective discount percentage = (190 / 1,000) * 100 = 19.

Verification / Alternative check:
You can also think in terms of average discount per rupee. Pritam saves Rs. 190 out of a possible Rs. 1,000 total marked price. That is a saving of 0.19 rupees per rupee of marked value, which directly translates to a 19% discount. This quick check confirms that our detailed calculation is consistent.

Why Other Options Are Wrong:
18 percent and 17 percent would both imply smaller total discounts than Rs. 190 on a marked price of Rs. 1,000.
16 percent corresponds to a discount of only Rs. 160, which contradicts the actual discount calculations.
20 percent discount would require Rs. 200 off, but the actual savings are Rs. 190, so that is also incorrect.

Common Pitfalls:
Some candidates mistakenly average the two discount rates of 10% and 20%, which does not work because the shirt and trousers contribute different amounts to the total price. Others forget to multiply the discounted price of one trouser by three. The safe strategy is to compute marked price and discounted price for each type of item individually, sum the totals, and then calculate the overall discount percentage from the combined figures.

Final Answer:
Pritam receives an overall effective discount of 19 percent on his total purchase.