Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

Re: Numbers added to a set [#permalink]
09 Jan 2011, 10:19

1

This post received KUDOS

Expert's post

gmatpapa wrote:

If numbers N and K are added to set X{2,8,10,12}, its mean will increase by 25%. What is the value of N^2+2NK+K^2 ?

A. 28 B. 32 C. 64 D. 784 E. 3600

Mean of {2,8,10,12} is mean=\frac{2+8+10+12}{4}=\frac{32}{4}=8 --> new mean thus should equal to 8*1.25=10, so \frac{2+8+10+12+n+k}{6}=10 (note that now we have the set of 6 terms not 4) --> n+k=60-32=28 --> n^2+2nk+k^2=(n+k)^2=28^2=784.

Re: If numbers N and K are added to set X{2,8,10,12}, its mean w [#permalink]
19 Sep 2013, 23:22

2

This post received KUDOS

Expert's post

gmatpapa wrote:

If numbers N and K are added to set X{2,8,10,12}, its mean will increase by 25%. What is the value of N^2+2NK+K^2 ?

A. 28 B. 32 C. 64 D. 784 E. 3600

You can also use the conceptual and deviation based methods to solve this.

Mean of set X{2,8,10,12} = 8 (Note that if we assume 8 to be the mean, 2 is 6 less than 8 and 10 and 12 are together 6 more than 8. Hence 8 must be the actual mean - the deviation approach)

When we add two numbers, the mean increases by 25% i.e. by 2. Had the two numbers been both 8, the mean would have stayed 8. But they have 2 extra for each of the 6 numbers so they must be a total of 8 + 8 + 6*2 = 28 (N + K)^2 = 28^2 = 784