Statistics Problem

Expert replies

briology: Junior | Next Rank: 30 Posts; Posts: 22; Joined: Sun Sep 18, 2011 1:14 am

by briology » Fri Sep 23, 2011 11:01 am

The average of 5 numbers is 6.8. If one of the numbers is multiplied by a factor of 3, the average of the numbers increases to 9.2. What number is multiplied by 3?

a. 1.5 b. 3.0 c. 3.9 d. 4.0 e. 6.0

This problem is a bit confusing for me. I understand how to solve it now (setup two equations), but still don't fully grasp the concept. Specifically, I don't understand why you can't find the difference between the two means and divide by 3 (which would give you 4 as your answer). Any help would be much appreciated!

Like this post

Source: Beat The GMAT — Problem Solving | Fri Sep 23, 2011 11:01 am

cans: Legendary Member; Posts: 1309; Joined: Mon Apr 04, 2011 5:34 amFollowed by: 123 members; Location: India; Thanked: 310 times; GMAT Score:750

by cans » Fri Sep 23, 2011 11:12 am

let sum of other 4 numbers=x and 5th number be y.
then x+y = 6.8*5 = 34
also x+3y = 5*9.2 = 46
2y = 12 and y=6

(take difference between means and divide by 3 is incorrect because mean is not multiplied by 3)

If my post helped you- let me know by pushing the thanks button

Contact me about long distance tutoring!
[email protected]

Cans!!

Like this post

gmatclubmember: Master | Next Rank: 500 Posts; Posts: 158; Joined: Sat Sep 03, 2011 10:31 amFollowed by: 2 members; Thanked: 29 times

by gmatclubmember » Fri Sep 23, 2011 11:13 am

briology wrote:The average of 5 numbers is 6.8. If one of the numbers is multiplied by a factor of 3, the average of the numbers increases to 9.2. What number is multiplied by 3?

a. 1.5 b. 3.0 c. 3.9 d. 4.0 e. 6.0

This problem is a bit confusing for me. I understand how to solve it now (setup two equations), but still don't fully grasp the concept. Specifically, I don't understand why you can't find the difference between the two means and divide by 3 (which would give you 4 as your answer). Any help would be much appreciated!

1. Summation of 5 no. = 5*6.8=34
When one no. is multiplied by 3 then the new mean is 9.2, so the new summation of the 5 nos. is 5*9.2=46.
So the sum of nos. increased from 34 to 46, that is by 12.
So multiplication of the no. increased the sum by 12. If that no. is x then
3x-x=12=>x=6.

Is OA E.

Cheers
Ami/-

Like this post

briology: Junior | Next Rank: 30 Posts; Posts: 22; Joined: Sun Sep 18, 2011 1:14 am

by briology » Fri Sep 23, 2011 2:37 pm

Thank you both for the replies! Although I'm still not 100% sure why you can't say 3x=12, when you know the increase was 12 and nothing changes except x becomes 3x

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 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