A,M

Expert replies

Imsukhi: Senior | Next Rank: 100 Posts; Posts: 36; Joined: Thu Jun 20, 2013 7:58 pm; Thanked: 1 times

by Imsukhi » Tue Jul 09, 2013 6:45 am

There are 25 arithmetic means between a and b such that the common difference is 4 and the sum of th means is 1375. find the value of a and b.

1) a-4,b-34
2) a-5,b-78
3) a-3,b-107,
4) a-7,b-113
5) none of above

Like this post

Source: Beat The GMAT — Problem Solving | Tue Jul 09, 2013 6:45 am

GMAT/MBA Expert

Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Tue Jul 09, 2013 7:08 am

Imsukhi wrote:There are 25 arithmetic means between a and b such that the common difference is 4 and the sum of th means is 1375. find the value of a and b.

1) a-4,b-34
2) a-5,b-78
3) a-3,b-107,
4) a-7,b-113
5) none of above

Unfortunately, the questions you are posting are either difficult to interpret, or they use terminology that is out of scope for the GMAT (or both). What is the source of this question?

"25 arithmetic means between a and b" Do you mean 25 terms between a and b (as in a sequence)?

"common difference": Not an expression that GMAT test-takers need to know.

I think this question involves a sequence in which every term is 4 greater than the term before it (e.g., 5, 9, 13, 17, ...). There are 27 terms in the sequence. The sequence begins with a and ends with b. The 25 terms in between a and b add to 1375. What is the value of a and b?

Is this interpretation correct?

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

Like this post

send2dar: Junior | Next Rank: 30 Posts; Posts: 14; Joined: Tue Jun 11, 2013 7:44 pm; Thanked: 1 times; GMAT Score:710

by send2dar » Sat Jul 13, 2013 6:54 am

For every 3 terms, the middle term is the arithmetic mean (in the arithmetic progression), in a series of N numbers (including a and b), there would be (N - 2) arithmetic means between a and b.

So, b should be a + 104 (as the common difference between two consecutive terms is 4 and b is 26th term after a, the difference between a and b should be 4 * 26 = 104).

In that case only option D is right (a = 3, b = 107).

Further, sums of these 25 terms would be 3*25 + 4*(25*26)/2 = 1375, this check confirms the answer...

I agree with Brent that these types of questions wont be part of GMAT in the language given... however if the question is worded differently, it can be a good candidate for inclusion to Quant section.

Cheers!

Thanks
---------------
V for Victory, V for Verbal. Only performance in Verbal section separates me from the Victory I want (Trying for 750+)

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 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