Optimal Answering Technique For MCQs!

Logic Level 2

Once Abhi had a chemistry test on reactivity, that he has not prepared for. He saw the following multiple-choice question, where only one choice was correct.

Which of the following is correct about element A?

1: It is more reactive than element B.
2: It is less reactive than element C.
3: It is less reactive than element D.
4: It is more reactive that element C.

Abhi does not know anything about elements A, B, C or D. Assuming that Abhi is a smart guy and thinks logically, what is the probability that Abhi will get this question correct?

Clarification: No two elements are equally reactive.

1

\dfrac{1}{2}

\dfrac{1}{3}

\dfrac{1}{4}

3 solutions

Nihar Mahajan
Mar 13, 2016

Choice 2 says "It is less reactive than element C", and
Choice 4 says "It is more reactive than element C" .

So obviously one of Choice 2 and Choice 4 is definitely the correct answer (because it is impossible to have both Choice 2 and 4 to be wrong).

But since Abhi knows nothing about elements, the probability that he chooses correct answer is $\frac{1}{2}$ .

Moderator note:

Great question. Eliminating MCQ options can increase your probability of guessing correctly.

Great! :)

A Former Brilliant Member - 5 years, 3 months ago

Thanks!! :rage:

Nihar Mahajan - 5 years, 3 months ago

Yeah same way, even I use a lot of logic in science practical mcqs although every time I know the answer but only to save time, like there some match the following or which are correct, sometimes the options are given foolishly that even if you check only 1 out of 4 statements given in the question you will get the answer.

Kushagra Sahni - 5 years, 3 months ago

Yeah, I once had a test about art where I was asked of shapes. One of the answers : a thing from a parallel universe. Although somewhat right, since PARALLEL universe, just no XD

Jase Jason - 5 years, 3 months ago

he have 3 choices. he can select a or c or one out of b and d as he can select only one probability is 1/3

Arth Singh - 5 years, 3 months ago

What if element A and element C were equally reactive. That makes both of those choices wrong.

Patrick Ford - 5 years, 3 months ago

I am assuming you asked this before the clarification lol

Chris Ruggieri - 5 years ago

I had the same logic.

Kevin Nigbur - 5 years, 3 months ago

I use this type of logic all the time!!

A Former Brilliant Member - 5 years, 2 months ago

Me too ;) ..

Nihar Mahajan - 5 years, 2 months ago

How can you say either choice 2 of choice 4 is correct

Department 8 - 5 years, 3 months ago

Element A is either more reactive than element C or less reactive than element C. So one of these two possibilities is definitely correct since they both are contradicting each other.

Nihar Mahajan - 5 years, 3 months ago

Then why not the other two options may be correct

Department 8 - 5 years, 3 months ago

@Department 8 – Because it is an MCQ question with only one correct answer.

Nihar Mahajan - 5 years, 3 months ago

@Nihar Mahajan – I meant any of the other two options

Department 8 - 5 years, 3 months ago

@Department 8 – We have already discovered that one of Option 2 and Option 4 is definitely correct. Since it is an MCQ question with only one correct answer , Option 1 and Option 3 are definitely wrong.

Nihar Mahajan - 5 years, 3 months ago

DarkMind S.
Sep 3, 2016

If Abhi is a good logician, then he knows that it comes down to 2 possibilities, .............Either A is more reactive than C, or it is Not.

Claudia Manotti
Mar 13, 2016

POICHè UNA SOLA SOLUZIONE è CORRETTA E POICHE' LA 2 O LA 4 SONO SICURAMENTE CORRETTE, LA 1 E L 3 SONO DAA ESCLUDERE E RESTA DA SCEGLIERE UNA TRA LA 2 E LA 4

Optimal Answering Technique For MCQs!

3 solutions

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