|1 Crore+ students have signed up on EduRev. Have you?|
As the name itself suggests, logical deduction questions require logical thinking. Every question starts off with a premise which might be of any one of the following types:
Type 1: If A Happens B Happens
This means that A leads to B, but does not mean the reverse, i.e., if B has happened, A must have happened. In such situations, A is a sufficient condition for B, but is not a necessary condition.
Let’s look at the following example:
If I go to a movie, I enjoy myself.
This would mean, that if I have gone to the movie, I will definitely enjoy myself. However, it does not mean that if I have enjoyed myself, I must have gone to the movie—there are so many ways of enjoying yourself.
Another example of this type would be:
If Amitabh acts in a movie, he will earn money.
This does not mean that if he has earned money, he must have acted in a movie.
Type 2: Only If A Happens B Happens
In this case, A is a necessary and sufficient condition for the occurrence of B. In this case, there is reversibility of the logic, i.e., if B has happened, A must have happened.
Only if Saurav plays the match, will he get a hundred.
If Saurav has got a hundred, he must have played the match.
Type 3: If A Happens B does not Happen
In this case, if A has happened, B does not happen. The opposite is also true, i.e., if B has happened, A must not have happened.
If Martina plays well, Sania will not win.
Type 4: If A does not Happen B will Happen
Again in this case, the reverse might not be true.
If Anand does not come, Kasparov will. This does not mean that if Kasparov comes, Anand will not come.
Type 5: Either A or B will Happen
One of the two has to happen. At the same time, the two events are exclusive of one another. If one happens, the other will not happen.
Either he becomes a TV star or he becomes a movie star.
Example 1. Shahrukh either acts as a villain, or he acts as a hero.
A. Shahrukh acts like a hero.
B. Shahrukh does not act like a villain.
C. Shahrukh acts like a villain.
D. Shahrukh does not act like a hero.
(a) Only CD
(b) Only BA
(c) CD and BA
(d) None of these
This question is based on an EITHER-OR Premise. Thus, we can see that CD is correct. Since, if he acts like a villain—(Statement C) he will not act like a hero (Statement D). Similarly, BA can also be seen to be true. Hence option (c) is correct.
Example 2. If I talk to my girl friends, then I do not need to take a pill for heartache.
A. I talked to my girl friends.
B. I did not need to take a pill for heartache.
C. I needed to take a pill for heartache.
D. I did not talk to my girl friends.
(a) Only AB
(b) Only DC
(c) Only CD
(d) AB and CD
This question falls under the category of if A happens, then B does not happen. However, if B has not happened, it does not mean that A has happened.
AB and CD are both logically correct.