[Math Revolution GMAT math practice question]
Let z be the harmonic mean of x and y. If 1/z=(1/2)((1/x)+(1/y)), which of the following is an expression for z, in terms of x and y?
A. 2xy / ( x + y )
B. 2( x + y ) / ( x - y )
C. 2( x - y ) / ( x + y )
D. 2( x + y ) / xy
E. xy / ( x + y )
Let z be the harmonic mean of x and y. If 1/z=(1/2)((1/x)+
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- Max@Math Revolution
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Aside: The GMAT doesn't expect test-takers to know the term harmonic mean.
If there were ever a question involving harmonic mean, the definition of the term would be included.
Here's the definition: https://www.investopedia.com/terms/h/ha ... verage.asp
Cheers,
Brent
If there were ever a question involving harmonic mean, the definition of the term would be included.
Here's the definition: https://www.investopedia.com/terms/h/ha ... verage.asp
Cheers,
Brent
- Max@Math Revolution
- Elite Legendary Member
- Posts: 3991
- Joined: Fri Jul 24, 2015 2:28 am
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=>
1/z = (1/2)(1/x + 1/y) = (1/2)( (x+y)/xy ) = (x+y)/(2xy)
Thus, z = 2xy / ( x + y ).
Therefore, A is the answer.
Answer: A
1/z = (1/2)(1/x + 1/y) = (1/2)( (x+y)/xy ) = (x+y)/(2xy)
Thus, z = 2xy / ( x + y ).
Therefore, A is the answer.
Answer: A
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- Max@Math Revolution
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We can solve this question without understanding the definition of a harmonic mean when we use the original condition 1/z = (1/2)(1/x + 1/y).Brent@GMATPrepNow wrote:Aside: The GMAT doesn't expect test-takers to know the term harmonic mean.
If there were ever a question involving harmonic mean, the definition of the term would be included.
Here's the definition: https://www.investopedia.com/terms/h/ha ... verage.asp
Cheers,
Brent
Math Revolution
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Score an excellent Q49-51 just like 70% of our students.
[Free] Full on-demand course (7 days) - 100 hours of video lessons, 490 lesson topics, and 2,000 questions.
[Course] Starting $79 for on-demand and $60 for tutoring per hour and $390 only for Live Online.
Email to : [email protected]