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# ISI Interview Experience

Some weeks ago, a co-author of this blog asked me to provide our interview experiences here. So here is my experience of B.stat interview at ISI:

Note: This was written by me couple of days after my interview.

## Pre-interview

My interview was scheduled on 2:30pm. I was supposed to come 30mins prior to that. There was two persons who checked our relevant documents and took some photocopies as per their procedure. Now we were directed to wait… wait… and wait…
Actually almost everyone had interview spanning about 40-50 minutes. So it was pretty late when I was called in. (It was 6:09pm. Yes, I remember it.)

## In the interview room

“Sir, may I come in?”
“Yeah, sure.”
(I walked to the table)
“So, you are – Aditya Ghosh?”
“Yes, sir.”
“Ramakrishna Mission, Rahara.”
“Rahara?”
“Yes.”
“Oh! Today morning another student came from your school…”
I said, “Sagar Ghosh?”
“Ah, Sagar. Classmate?”
“Yes.”
“Okay. So let me ask some questions about (yourself)…” (He looks down, on a paper) “What was your HS percentage?”
“91%.”
“Maths?”
“100.”
“Ah… I think 87…87.1%.”
“And maths?”
“100.”
“Ok. How do you think you perform in the written exam?” (His face was notable – as if he was judging how much I know myself!)
I said, “Ah, that Q.4 area question, I couldn’t finish it…”
He interupted, “You didn’t tried it or couldn’t do it for lack of time?”
I said “Sir, I didn’t have time.”
“Alright. And how was the objective paper? How many do u think u have done correct, out of 30?”
“Around 25, I think.”
Then he noded saying “Okay” and looked on his right. Then another sir (from his right) asked me “Did you give jee advance?”
“No…no, sir.”
“And the joint of WB board(WBJEE)?”
“No, sir.”
“Which exams did you give?”
“Sir I gave the ISI entrance and the CMI entrance.”
“Aa…Yes, I got selected.”
“Okay” the first sir said, “We will ask you question” (confirming with the 2nd sir by gesturing) and then told me, “So which topic would you like…”
“…Aa…Number theory.”
Then he looked on his left. Another sir started giving me a question.

“Umm. Suppose…”
I stood up saying “Should I go to the board?”
“Yes.”
“Write down: Let the complex number $a+ib$ ($a,b\in\mathbb{Z}$) have the property that there exists $c+id (c,d\in\mathbb{Z})$ such that $(a+ib)(c+id)=1.$ Find all such complex numbers.” I thought for a while, and then said “If we take modulus on both sides, we get $\vert (a+ib)(c+id)\vert=1$And $\vert (a+ib)(c+id)\vert=\vert (a+ib)\vert\vert(c+id)\vert=\sqrt{a^2+b^2}\sqrt{c^2+d^2}.$ So we must have $a^2+b^2=1$ as well as $c^2+d^2=1$ since $a,b,c,d$ are all integers. Now, if one of $a^2$ or $b^2$ is greater than 1 then not possible. In this way we get $(\pm 1,0)$ and $(0,\pm 1)$ are the only possibilities for $(a,b)$. So all possible candidates are $\pm 1$ and $\pm i.$

Now the first sir affirmed with the sir who asked the question (nodding heads, saying “Ok..”) and then the first sir told me “Okay…” with “Now you can leave” on his face! I confirmed by saying “Should I go?”.
He said, “Yes, you can leave.”
I took my documents from the table and left the room.
I can’t recall the exact duration, but I am pretty sure it was very less (maybe 10 minutes).

## My suggestions for the interview

1. Don’t dare to lie, specially about your credentials. They have all the documents on their table.
2. Behave politely. They are very very friendly. (This does not mean you should speak too frankly, you must be respectful.) Specially, don’t be over-smart even if they ask you easy questions.
3. Know your worth. If they are asking “What do you think, how much did you do correctly in the objective paper?” Answer specificly. “Around 20” is far more safer than saying “I attempted 27, of them I was sure of 25…but later I recognised I did silly mistakes and 5 of them seemed to be wrongly answered.”
4. Keep calm, be confident. Don’t get nervous. Nervousness always spoils your performance.
5. Don’t use big theorems to prove small results. Keep your solution as simple as possible.

Note: The conversation is not 100% accurate – I don’t have that strong memory. But I tried to write as much as I can recall.

Another note: My experience vary with others. For example, I can not tell you about the hints that they give when you are struck. (Of course, I consider myself fortunate enough, for not being able to tell this.) But what I can tell you is that, if you give the subjective paper well then you are supposed to have shorter and easier interview than others. (I did, what most people say, 7.25 questions: I just could not finish some calculations in Q.4 (the area problem) and I failed to solve part (a) of Q.8.)

Afterwords: Being a student at ISI Kolkata, now I know that the professor who started my interview (referred as “first sir” above) is Mr. Alok Goswami and the professor who gave me the number-theoretic problem, is Mr. Mrinal Kanti Das. Unfortunately, I don’t recall the faces of other persons present in the interview board at the time of my interview.

P. S. This blog is no longer maintained by me. You can mail me at ghoshadi26@gmail.com or visit my other blog: http://www.ghoshadi.wordpress.com

## 5 thoughts on “ISI Interview Experience”

1. Saptarshi Dey says:

The problem they asked in the interview was quite remarkable!
I think you must have observed that,the solutions you got are nothing but the 4th roots of unity!!!!!!

Liked by 1 person

2. Can you please also provide how you studied for ISI/CMI exam as well

Liked by 2 people

3. Apratim Sarkar says:

If I give all the joint exams can I tell them??

Liked by 1 person

1. Apratim Sarkar says:

Hello I am APRATIM SARKAR Of your Monday evening batch of RSM

Liked by 1 person