If the average (arithmetic mean) of $x, y$ and $15$ is $9,$ and the average of $x, 2y$ and $2$ is $7,$ then

If the average (arithmetic mean) of $x, y$ and $15$ is $9,$ and the average of $x, 2y$ and $2$ is $7,$ then $y =$

A. 5
B. 6
C. 7
D. 8
E. 9

Answer: C

Source: Magoosh

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psarma: Junior | Next Rank: 30 Posts; Posts: 24; Joined: Wed Jun 29, 2011 1:47 am

Re: If the average (arithmetic mean) of $x, y$ and $15$ is $9,$ and the average of $x, 2y$ and $2$ is $7,$ t

by psarma » Thu Oct 01, 2020 3:44 pm

Average of x,y & 15 is 9
i.e (x+y+15)/3 = 9
or x+y=12

Also, average of x,2y & 2 is 7
i.e (x+2y+2)/3 = 7
or x+2y = 19

Subtracting 1st equation from 2nd equation,
we get y = 7

Option C

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GMAT/MBA Expert

Scott@TargetTestPrep: GMAT Instructor; Posts: 7244; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

Re: If the average (arithmetic mean) of $x, y$ and $15$ is $9,$ and the average of $x, 2y$ and $2$ is $7,$ t

by Scott@TargetTestPrep » Tue Oct 06, 2020 3:15 am

M7MBA wrote: ↑
Thu Oct 01, 2020 6:54 am
If the average (arithmetic mean) of $x, y$ and $15$ is $9,$ and the average of $x, 2y$ and $2$ is $7,$ then $y =$

A. 5
B. 6
C. 7
D. 8
E. 9

Answer: C

Solution:

We can create the equations:

(x + y + 15)/3 = 9

and

(x + 2y + 2)/3 = 7

Subtracting the first equation from the second, we have:

(y - 13)/3 = -2

y - 13 = -6

y = 7

Answer: C

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