How to solve multiple choice questions in IIT-JEE?

This is ten percent luck, twenty percent skill
Fifteen percent concentrated power of will
Five percent pleasure, fifty percent pain
And a hundred percent reason to remember the name!

“IIT-JEE” – the toughest exam in the world at 18 years of age. Well, lets leave all that blah blah. If you are actually reading this article, then i guess you don’t need to be told anything about it. You already know the numbers – 5 lakh applicants, 2% success rate and all that. Now, in case you have really been studying your ass off for IIT, kudos to you and your courage. Now, let’s get to the point.

I am no stud in the field of engineering studies. I was one of those types who never studied anything seriously. I never followed any textbook (H.C.Verma, loni, M.L.Khanna and all), bunked 70% of my classes and made every possible effort to get to enjoy my life in my +2.  I am the so-called lucky guy who just managed to scrape through into an IIT. Hence, i am no expert to advise people on giving tips to study. But still, if i managed to get through, that means i struck gold somewhere else. That’s what I am discussing here.

For the fact, all the engineering exams in India are objective. Now there are two ways to crack it – either know the concept or know all the wrong answers. In the exam, nobody cares how you circled the bubble. The administrators don’t care if you knew the concept or cheated or circled it blindly or made a fluke. What matters is only the circling of the correct bubble, no matter how you do it. And SENSIBLE GUESSING DOES HELP A LOT IN GAINING THOSE MARKS.

After all, negative marking is just meant to discourage blind guessing only, nothing else. But if you are able to guess sensibly, you will never receive loss due to it. Imagine this yourself - all the exams have 4 options to each questions and, believe it or not, all the answers are equally distributed among all the four options i.e. a, b, c, and d (this is true for all exams- be it your phase test, test series, AIEEE or even IIT-JEE). Now even in the worst case scenario (marking scheme: plus 3,minus 1), if you mark all your blind guesses as, say option-“a”, even then the net difference in your marks will be ZERO.

Surprised!!?? Suppose you made guesses in “x”-number of questions and marked them all as option-“c”. Going by the law of probability, 75% of your guesses will be wrong and 25% will be right. Lets calculate your total by that:

[(X/4) x (+3)] – [(3X/4) x (-1)] =zero. Hence there will be zero addition to your score in the worst case which is true because the administrators never want anyone to lose out because of probability. So they equally distribute the options among all the answers. Now suppose the marking scheme is plus 4, minus 1, as in many exams like DCE, you can actually GAIN 1 MARK for ever four guessed answers by you. Ain’t that free marks??!! :-P

Here are some of the tricks-

1)  Highest and lowest: In a question where numerical values are the answers, the highest and value will never be the correct answers. Weird as it may seem, but it is true for atleast 60% of the cases. So, if you don’t know the way to solve question, try staying away from the extreme values of answers. It might just help you.

2) Two or zero: Whenever in doubt between two of the options, try gambling on one of them. When you have managed to cross out two options, try going for one from the remaining two options. It works.

3) No negatives: For those questions which don’t carry any negative marking (eg: match the following, multiple answers questions which appear ever year in IIT-JEE), go for them even if you don’t even know an inch of the concept. DO NOT EVER LEAVE THEM UNATTEMPTED. If the thing has no discouragements, then why should we be a fool to leave free gambles?

4) Same and different: This applies for those questions which have options in which they play in units and values. Eg: suppose the options for a heat and thermodynamics question are:

(a) 120 K ; (b) 130 C ; (c) 120 C (d) 110 C

Now, since 3 of the options are given in degree Celsius, therefore answer will definitely be in degree Celsius. Now since the value 120 is given in both celsuis and Kelvin, therefore 120 is the numerical answer. Hence, going by the above two logics, the answer will be option-(c) 120 C. Trust me or not, it works in 80% of the cases!

5) Mathematical extremes: Everytime, we do find questions in maths which ask us to either find the range or domain of a function, and the options are generally given as:

(a) [0,1) U (2,3) ; (b) (0,1) U (2,3] ; (c) [0,1] U [2,3] ; (d) (0,1) U (2,3)

As you must have already understood, simply try to test the function on the extreme values i.e.0,1,2,3. You don’t need to solve the whole dam function. Simply see if these 4 values satisfy the function and you will be able to get to the answer.

6) Dimensions: This is one field where the administrators show their complete ignorance. Such types of questions have very stupid options that you feel like laughing on them. Suppose you have a question to find the velocity of an object in an electromagnetic field in some weird orientation with field values as E and B. The options will be something like

(a) (2E/B)^1/2 ; (b) (2B/E) ; (c)  (2E/B) ; (d) (2B/E)^1/2

Now, by simply analysing the dimensions you can tell the answer. Electric field has dimensions (M¹L¹T^-3A^-1) and magnetic field has dimensions (M¹L⁰T^-2A^-1). Simply, you can see that E/B will give you (L¹T^-1) which is dimension of velocity whereas square-root of (E/B) will give root of velocity. Hence, the answer will obviously be option-(c). The “2E” will take care of itself. Dimensional analysis really helps. It helps at a lot of places.

7) Value putting: This applies for questions where we have to find the general expression for something. Suppose you have to find the expression for pressure on a bubble of radius-R when it is at a height h from the ground level in the container which has water upto a height L. (i am just taking a general and easy example, not an exact one.) So, let the options be

(a) P + [pg(L-h)/LR] ; (b) P + [pgLR/(L-h)] ; (c) P + [pgR(L-h)/L] ; (d) P + [pg(L-h)(L-R)/L)

Now, if you would have noticed, you can simply leave out option-(a) by simply checking its dimensions. The dimensions of second term are not that of pressure but of pressure per unit area. Even if you ignore that, we know that pressure at the surface of water must be P and must be (P + pgL) at the base of container. So we have two cases:

At,h=0; pressure=(P + pgL)  and  at,h=L; pressure=P. On putting these two values of “h” in these options, we can clearly see that option-(d) is the correct answer.

(More in next part. Stay tuned)

In case you want to test all these things, take up an MCQ set of a topic which you have not studied and try all these logincs on those questions and see the score that you get. I indirectly practiced these things and they really helped me. I got 30 extra marks in IIT-JEE by the same approach!!

Well, now i am a bit tired by writing and need some sleep too. So I am stopping here. The next part will be out in 4-5 days. In case you liked the post, please comment and give your feedback. In case you want any advice, you can contact me at my email id on my blog profile. Remember, the exam tries to test our knowledge and understanding, but sometimes it just forgets to maintain the logic in the options. (^_^) (*_*)

Click here for Part-2