A shop, which sold same marked price shirts, announced an offer - if one buys three shirts then the fourth shirt is sold at a discounted price of ₹ 100 only. Patel took the offer. He left the shop with 20 shirts after paying ₹ 20,000. What is the marked price of a shirt?
Show Hint
In offer-based arithmetic problems, always group purchases according to the offer cycle (like here in blocks of 4). This simplifies the problem and avoids mistakes in counting discounts.
Step 1: Understanding the offer
The shop has an offer: buy 3 shirts at full marked price (M), and get the 4th shirt at a discounted price of only ₹ 100.
Thus, the cost of every block of 4 shirts = \(3M + 100\).
Step 2: Finding how many sets of 4 Patel bought
Patel bought a total of 20 shirts.
Since the offer works in sets of 4 shirts, we divide:
\[
20 \div 4 = 5
\]
So, Patel availed the offer exactly 5 times.
Step 3: Writing total cost equation
Cost of 1 set of 4 shirts = \(3M + 100\).
Cost of 5 sets (20 shirts) = \(5 \times (3M + 100)\).
We are told this equals ₹ 20,000.
So,
\[
5(3M + 100) = 20000
\]
Step 4: Simplifying
Divide both sides by 5:
\[
3M + 100 = 4000
\]
Subtract 100:
\[
3M = 3900
\]
Divide by 3:
\[
M = 1300
\]
Step 5: Final Answer
The marked price of each shirt is ₹ 1300.
\[
\boxed{1300}
\]