System design interview questions for freshers, with answers

With the Series A in, Meera Kulkarni hires freshers, and Arjun Nair now sits on the interview panel.

Shreya, a fresher from Nagpur, is asked to design a ticket app. In two minutes she draws a clean, correct-looking diagram from memory, then goes quiet. She scores low. “But the picture was perfect,” Arjun says.

Zoya Mirza shows him the score sheet: no row for the picture. In Arjun’s own practice interview, he drew from memory too. Zoya stopped him at two minutes: “What must it do, and for how many people?”

The rows are blank: Arjun must write the panel’s rubric, the list of what earns marks. “If not the picture,” Zoya asks, “what do we mark?” Arjun looks at the empty sheet.

Fresher and SDE-1 rounds often ask concept questions about parts you have learnt, and sometimes a small design, though it depends on the company. SDE-1 is the first software engineer level at many companies.

Remember one line: the interviewer marks the reasoning you say out loud, not a memorised diagram. That reasoning runs in five parts.

• Requirements: ask what it must do and how many use it at the peak.
• Estimates: rough numbers, saying each assumption.
• High-level design: sketch the main path, with a trade-off for each choice.
• Closer look: pick one box and say how it works, scales and fails.
• Wrap-up: say what fails first, and what you would do.

A common plan gives those five parts 45 minutes: 5 + 5 + 15 + 15 + 5 = 45. The closer look has its own name.

• A friend leaves a placement round puzzled: they asked what happens when you open a ticket app. That was a concept question about the round trip.
• Another friend memorises a chat-app diagram, then freezes at “now make it work on a slow network”. A memorised picture cannot bend.
• At a college quiz, the host says “show your working”, and the team that explains beats a lucky guess. Design rounds are often marked the same way.

It depends on the company. Some ask concept questions, some a small design, and some none. Others ask an LLD round, on the code inside one box, such as “design a movie booking app”. The method helps in all of them.

The 45 minutes follow the viva’s rhythm. First come five minutes of asking and twenty on the rough sheet. Then fifteen of follow-up questions and five to wrap up.

You ask before you draw: what must it do, and how many people at the peak? In Arjun’s practice round, Zoya answers: pick a seat, pay, get a ticket. The noon peak is about 16,700 requests a second.

What just happened? The first five minutes drew no boxes, only scope, like asking the examiner what the question expects. Every later box ties to a number.

Eight questions are common in fresher rounds, and each has a short outline you can say in about a minute.

A weak answer names tools without a number, claims a free lunch, or says nothing about what fails. It is the student who recites the page, then goes quiet.

What just happened? Each weak answer skipped a number, denied a failure or repeated a myth.

Rounds above fresher level often ask about replication lag, shard keys, consistent hashing, retry storms and region failure, with numbers. It is the same viva, harder, and it depends on the company.

Keep lesson 7’s working ready: 5 lakh people × 20 requests = 1 crore in the 600-second noon sale, about 16,700 a second. Assume about 200 a second per server: that is 83.5, so about 84 servers before a cache.

That number also picks your deep dive. The seat hold takes the noon load, so say how it scales and what happens to held seats if its store restarts.

Try it yourself

1. 1

   Pick one card

   Choose one of the eight, such as the cache one.

2. 2

   Answer against the clock

   Answer aloud and record yourself. Aim for about a minute, with 3 minutes as the limit.

3. 3

   Mark yourself

   Tick five lines: plain definition, a number, a trade-off, what fails, no tool without a reason.

4. 4

   Go again

   Repeat once and fix your weakest line. You got it if four of five lines are ticked on the second try, without reading the card.

Back to the empty sheet. Arjun fills the rows, and Zoya reads them aloud: asks about requirements, estimates, sketches the main path, names trade-offs, says what fails. Still no row for the picture.

Shreya gets a practice slot. She opens with, “How many people at the noon peak, and what must never go wrong?” Her diagram is the same, but her marks change. Arjun reruns his own practice interview and passes.

So the panel marks the method you say out loud, not the picture. This course teaches HLD, the boxes and arrows. Some companies also add an LLD round, and lesson 20’s double booking fix helps there. Now design something yourself, end to end.