Lesson: The Fundamental Counting Principle

Comment on The Fundamental Counting Principle

Question at http://gmatclub.com/forum/a-palindromic-number-reads-the-same-forward-and-backward-214196.html is not clear to me. Could you please help me on this?

How many 6-digits number are Palindromic numbers? A Palindromic number reads the same forward and backward, example 12121.
A) 100
B) 610
C) 729
D) 900
E) 1000
gmat-admin's picture

I'm not a huge fan of that question because it first starts by talking about 6-digit numbers and then gives an example of a 5-digit number that works. However, my solution appears on that same page.
The basic idea is that, once we have selected the first 3 digits of the number, the last 3 digits automatically follow.
For example, if the first 3 digits are 356---, then (to be a palindrome), the last 3 digits must be ---652, so we get the number 356652.
Likewise, if the first 3 digits are 197---, then (to be a palindrome), the last 3 digits must be ---791, so we get the number 197791.

Hey Brent! I love your videos so much. They are of great help to me!
My question is, how commonly is this topic tested on the GMAT? Is this a frequently tested topic? Is it advisable to skip this one topic out of all others or will it hurt my score significantly?

gmat-admin's picture

Glad you like the videos!

Counting questions aren't that common on the GMAT.

The number of questions YOU see on test day will depend on how well you're doing on the quantitative section. If you're doing really well, you MIGHT see 2 or 3 counting questions. If you're not doing well, you'll see FEWER counting questions.

If your prep time is limited, I suggest that you master the The Fundamental Counting Principle strategy, since it can be used for the majority of counting questions on the GMAT.

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