**EOK: Examiner-only-knows**

Let me give you an example. A bell tolls once every 20 seconds, another tolls once every 30 seconds. If both of them ring at the same time, how many time will they ring togrther in thr first hour?

Now, they will ring together once every minute. But the cheap-tricks-of-examiners book says that the answer for this question can be 61 instead of 60. You can answer this question only if you know the examiner. Sometiem you cannot answer it even if you know the examiner. These are the Examiner-Only-Knows questions

**The next category is GOK:**

Let me give you a sample. The difference between the lengths of the diagonals of a paralleogram inscribed in a circle is 2 cms, fidn the area of the parallelogram.

Now, a parallelogram inscribed in a circle has to be a rectangle. And the diagonals of a rectangle are equal. So, it is clear that even the examiner does not know the answer to this one. God Only Knows – GOK

**The third category is intersting. And this is probably the most useful as well. This is the Now-you-now category**

There was/is a legendary professor of organic Chemistry named Govindarajan in Chennai who used to train students for the JEE in the 80’s, 90’s and 00’s. He was an elderly gentleman even in the late 90’s, and wonderful as he was in teaching, he was also laidback about exams, scores, records, performance-trackers and the like. After one of his famous exams – bunch of students had some issues with the paper because it had some questions being beyond what he had taught in class. (Imagine 17-year olds anxious to tell themselves they messed up only because they hadnt been thought that bit). He looked at said questions “I did not teach you this?! You did not know about this?” with an incredulous look on his face. This slowly gave way to a wry smile and he said “Well, well, well. Now You Know.”

There will always be Now-you-know questions in exams. Stuff that you did not know before, but is probably an important tidbit.

Try this one – A six-digit number N of the form ‘abcabc’ where a, b, and c are digits from 0 to 9 has exactly 16 factors, how many values can N take?

If you know that a number ‘abcabc’ is ‘abc’ * 1001 and that 1001 = 7 * 11 * 13, this question becomes easy. If you do not know this and you see this in a mock CAT paper, it is probably a good time to say “Now I know” (after you review the paper):)

This is why it is important to aggressiely review your mock CATs and not just fixate on the percentiles.