Number Properties | The functions f and g are defined for al - The Beat The GMAT Forum

Number Properties | The functions f and g are defined for al

Expert replies

richachampion: Legendary Member; Posts: 698; Joined: Tue Jul 21, 2015 12:12 amFollowed by: 26 members; Location: Noida, India; Thanked: 32 times; GMAT Score:740

by richachampion » Thu Oct 06, 2016 4:15 pm

The functions f and g are defined for all the positive integers n by the following rule: f(n) is the number of positive perfect squares less than n and g(n) is the number of prime numbers less than n. If f(x) + g(x) = 16, then x is in the range:

A. 30 < x < 36
B. 30 < x < 37
C. 31 < x < 37
D. 31 < x < 38
E. 32 < x < 38

R I C H A,
My GMAT Journey: 470 â†’ 720 â†’ 740
Target Score: 760+
[email protected]
1. Press thanks if you like my solution.
2. Contact me if you are not improving. (No Free Lunch!)

Like this post

Source: Beat The GMAT — Problem Solving | Thu Oct 06, 2016 4:15 pm

richachampion: Legendary Member; Posts: 698; Joined: Tue Jul 21, 2015 12:12 amFollowed by: 26 members; Location: Noida, India; Thanked: 32 times; GMAT Score:740

by richachampion » Thu Oct 06, 2016 4:16 pm

OA : C

R I C H A,
My GMAT Journey: 470 â†’ 720 â†’ 740
Target Score: 760+
[email protected]
1. Press thanks if you like my solution.
2. Contact me if you are not improving. (No Free Lunch!)

Like this post

GMAT/MBA Expert

[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members; Location: Palo Alto, CA; Thanked: 2867 times; GMAT Score:800

by [email protected] » Thu Oct 06, 2016 6:24 pm

Hi All,

We can use the answer choices to our advantage on this question (by determining if number of possible or impossible, we can eliminate answer choices).

Let's start by TESTing X=31. According to the prompt...

f(31) = number of perfect squares less than 31 = {1, 4, 9, 16, 25] = 5
g(31) = number of primes less than 31 = {2, 3, 5, 7, 11, 13, 17, 19, 23, 29} = 10

f(31) + g(31) = 15; we're told that it's SUPPOSED to be 16 though, so X CANNOT be 31. Eliminate Answers A and B.

Next, let's TEST X = 37. According to the prompt...

f(37) = number of perfect squares less than 31 = {1, 4, 9, 16, 25, 36] = 6
g(37) = number of primes less than 31 = {2, 3, 5, 7, 11, 13, 17, 23, 29, 31, 3} = 11

f(37) + g(37) = 17; we're told that it's SUPPOSED to be 16 though, so X CANNOT be 37. Eliminate Answers D and E.

Final Answer: C

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

Like this post

richachampion: Legendary Member; Posts: 698; Joined: Tue Jul 21, 2015 12:12 amFollowed by: 26 members; Location: Noida, India; Thanked: 32 times; GMAT Score:740

by richachampion » Thu Oct 06, 2016 7:00 pm

[email protected] wrote: Final Answer: C

GMAT assassins aren't born, they're made,
Rich

Thanks Mr. Rich,

I find this question quite irritating. whats your Opinion about this question?

R I C H A,
My GMAT Journey: 470 â†’ 720 â†’ 740
Target Score: 760+
[email protected]
1. Press thanks if you like my solution.
2. Contact me if you are not improving. (No Free Lunch!)

Like this post

MartyMurray: Legendary Member; Posts: 2135; Joined: Mon Feb 03, 2014 9:26 amFollowed by: 140 members; Location: https://martymurraycoaching.com/; Thanked: 955 times; GMAT Score:800

by MartyMurray » Thu Oct 06, 2016 9:20 pm

richachampion wrote:I find this question quite irritating. whats your Opinion about this question?

This question is a little boring, and it's not very sophisticated.

At the same time, the GMAT is often a test of skill in just plain getting things done, and answering this question is about pretty much just getting something done.

So maybe the thing to do with a question like this one is just to see it for what it is, come up with a way to get to the answer, and GET IT DONE.

Enjoy the game!!!

Marty Murray
Perfect Scoring Tutor With Over a Decade of Experience
MartyMurrayCoaching.com
Contact me at [email protected] for a free consultation.

Like this post

GMAT/MBA Expert

[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members; Location: Palo Alto, CA; Thanked: 2867 times; GMAT Score:800

by [email protected] » Fri Oct 07, 2016 9:13 am

Hi richachampion,

Regardless of whether you 'like' a question or not, you have to remember that the Quant section of the GMAT is NOT, strictly-speaking, a "math test." As such, you're going to face questions that really are NOT about 'testing' you math skills - they're about testing your 'critical thinking' skills (a variety of DS questions exist for exactly this purpose). Ultimately, when dealing with a Quant question, I consider every piece of information that I'm given to work with (including the answer choices) and look for the easiest/most-efficient approach to get to the correct answer. In some cases, that means "just do math", but more often there's a Tactic, pattern or logic-based approach that will work really well. Even the nastiest questions are still based on patterns and rules, so even if I don't immediately see an obvious approach, there are details in the prompt that will remind me of OTHER questions that I've already answered - so I can 'play around' a bit with the prompt and likely find the pattern that I need to know to properly answer the question.

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

Like this post

richachampion: Legendary Member; Posts: 698; Joined: Tue Jul 21, 2015 12:12 amFollowed by: 26 members; Location: Noida, India; Thanked: 32 times; GMAT Score:740

by richachampion » Fri Oct 07, 2016 2:12 pm

[email protected] wrote:Hi richachampion,

Regardless of whether you 'like' a question or not, you have to remember that the Quant section of the GMAT is NOT, strictly-speaking, a "math test." As such, you're going to face questions that really are NOT about 'testing' you math skills - they're about testing your 'critical thinking' skills (a variety of DS questions exist for exactly this purpose). Ultimately, when dealing with a Quant question, I consider every piece of information that I'm given to work with (including the answer choices) and look for the easiest/most-efficient approach to get to the correct answer. In some cases, that means "just do math", but more often there's a Tactic, pattern or logic-based approach that will work really well. Even the nastiest questions are still based on patterns and rules, so even if I don't immediately see an obvious approach, there are details in the prompt that will remind me of OTHER questions that I've already answered - so I can 'play around' a bit with the prompt and likely find the pattern that I need to know to properly answer the question.

GMAT assassins aren't born, they're made,
Rich

__________________

Marty Murray wrote:
This question is a little boring, and it's not very sophisticated.

Thanks Mr. Rich and Mr. Murray. This question was not tough, but a boring one.

R I C H A,
My GMAT Journey: 470 â†’ 720 â†’ 740
Target Score: 760+
[email protected]
1. Press thanks if you like my solution.
2. Contact me if you are not improving. (No Free Lunch!)

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

563 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (563 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review