If x,y and k are positive numbers such that (x/x+y)10 + (y/x+y)20 = k and if x<y, which of the following could be the value of k?
a. 10
b. 12
c. 15
d. 18
e. 30
This question if from OG question no-148
Is there a quicker way to solve this problem?
value of k
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(x/x+y)*10 + (y/x+y)*20, Can be simplified as shown below.
(x/x+y)*10 + (y/x+y)*10 + (y/x+y)*10
((x+y)/(x+y))*10 + (y/x+y)*10
10 + (y/x+y)*10
0 < x < y and x,y are positive numbers. The the boundaries are x=0 and x=y
10 + (y/y+y)*10 < 10 + (y/x+y)*10 < 10 + (y/0+y)*10
15 < 10 + (y/x+y)*10 < 20
The only number which is between 15 and 20 is 18, IMO Option D
(x/x+y)*10 + (y/x+y)*10 + (y/x+y)*10
((x+y)/(x+y))*10 + (y/x+y)*10
10 + (y/x+y)*10
0 < x < y and x,y are positive numbers. The the boundaries are x=0 and x=y
10 + (y/y+y)*10 < 10 + (y/x+y)*10 < 10 + (y/0+y)*10
15 < 10 + (y/x+y)*10 < 20
The only number which is between 15 and 20 is 18, IMO Option D
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You can do this problem very quickly without doing any math. If you look closely at the problem, you'll see that the equation is simply a weighted average of 10 and 20.
x/(x+y) + y/(x+y) will equal 1 --> x/(x+y) + y/(x+y) = (x+y)/(x+y) = 1
So we can simplify this equation by saying x/(x+y) = X and y/(x+y) = Y where X + Y = 1. This now writes 10X + 20Y = k. This is the weighted average equation above. Since X + Y = 1 and X and Y are both positive, they will both be percentages and k will be between 10 and 20.
Since we know that x < y, we know that Y has to be greater than 50%. This also means that k has to be between 15 and 20. The only answer that fits that description is D.
x/(x+y) + y/(x+y) will equal 1 --> x/(x+y) + y/(x+y) = (x+y)/(x+y) = 1
So we can simplify this equation by saying x/(x+y) = X and y/(x+y) = Y where X + Y = 1. This now writes 10X + 20Y = k. This is the weighted average equation above. Since X + Y = 1 and X and Y are both positive, they will both be percentages and k will be between 10 and 20.
Since we know that x < y, we know that Y has to be greater than 50%. This also means that k has to be between 15 and 20. The only answer that fits that description is D.
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I posted a solution here:nidhis.1408 wrote:If x,y and k are positive numbers such that (x/x+y)10 + (y/x+y)20 = k and if x<y, which of the following could be the value of k?
a. 10
b. 12
c. 15
d. 18
e. 30
This question if from OG question no-148
Is there a quicker way to solve this problem?
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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
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