Brent@GMATPrepNow wrote:Here's a 700-level question I just made up:
The average (arithmetic mean) of y numbers is x. If z is added to the numbers, the new average (arithmetic mean) will be z-5. What is the value of z in terms of x and y?
A) x + 5/y + 5
B) (xy + 5y)/(y - 1)
C) (xy - 5)/(y+1)
D) x/(y+1) - 5y
E) x - 5/y
Let z=5, implying that -- after 5 is added to the original numbers -- the resulting average = z-5 = 5-5 = 0.
For the resulting average to be 0, the sum after 5 is added must also be equal to 0.
Implication:
The sum of the original numbers must be -5.
Let y=1 and x=-5, with the result that the sum of the original numbers = (number of numbers)(average of the numbers) = (1)(-5) = -5.
The question stem asks for the value of z=5. This is our target.
Now plug y=1 and x=-5 into the answer choices to see which yields our target of 5.
Only
A works:
x + 5/y + 5 = -5 + 5/1 + 5 = 5.
The correct answer is
A.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at
[email protected].
Student Review #1
Student Review #2
Student Review #3
