BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

If 0 < x < 1 and y > 1

Expert replies
Source: — Problem Solving |

by Jay@ManhattanReview » Mon Jun 12, 2017 5:26 am
jack0997 wrote:If 0 < x < 1 and y > 1, [√{x + y - 2√(xy)} + √{x + y + 2√(xy)}] =

(A) √x
(B) 2√x
(C) √y + √x
(D) √y
(E) 2√y

OA E
An efficient approach for such questions is by plugging in smart values for x and y.

Since we have to deal with √xy, the values chosen for x and y must be such that √xy is not an ugly number.

Say x = 1/4 and y =4. This makes √xy = √(1/4)*4 = √1 = 1. This works.

Just plug-in these values and check which option renders the correct answer.

Hope this helps!

Download free ebook: Manhattan Review GMAT Quantitative Question Bank Guide

-Jay
_________________
Manhattan Review GMAT Prep

Locations: New York | Bangkok | Abu Dhabi | Rome | and many more...

Schedule your free consultation with an experienced GMAT Prep Advisor! Click here.
Join the discussion

by jack0997 » Tue Jun 13, 2017 12:54 am
Jay@ManhattanReview wrote:
jack0997 wrote:If 0 < x < 1 and y > 1, [√{x + y - 2√(xy)} + √{x + y + 2√(xy)}] =

(A) √x
(B) 2√x
(C) √y + √x
(D) √y
(E) 2√y

OA E
An efficient approach for such questions is by plugging in smart values for x and y.

Since we have to deal with √xy, the values chosen for x and y must be such that √xy is not an ugly number.

Say x = 1/4 and y =4. This makes √xy = √(1/4)*4 = √1 = 1. This works.

Just plug-in these values and check which option renders the correct answer.

Hope this helps!

Download free ebook: Manhattan Review GMAT Quantitative Question Bank Guide

-Jay
_________________
Manhattan Review GMAT Prep

Locations: New York | Bangkok | Abu Dhabi | Rome | and many more...

Schedule your free consultation with an experienced GMAT Prep Advisor! Click here.
Thank you, Jay. It was helpful. Could you pl. tell me the algebraic route?
Join the discussion

by Jay@ManhattanReview » Tue Jun 13, 2017 3:41 am
jack0997 wrote:
Jay@ManhattanReview wrote:
jack0997 wrote:If 0 < x < 1 and y > 1, [√{x + y - 2√(xy)} + √{x + y + 2√(xy)}] =

(A) √x
(B) 2√x
(C) √y + √x
(D) √y
(E) 2√y

OA E
An efficient approach for such questions is by plugging in smart values for x and y.

Since we have to deal with √xy, the values chosen for x and y must be such that √xy is not an ugly number.

Say x = 1/4 and y =4. This makes √xy = √(1/4)*4 = √1 = 1. This works.

Just plug-in these values and check which option renders the correct answer.

Hope this helps!

Download free ebook: Manhattan Review GMAT Quantitative Question Bank Guide

-Jay
_________________
Manhattan Review GMAT Prep

Locations: New York | Bangkok | Abu Dhabi | Rome | and many more...

Schedule your free consultation with an experienced GMAT Prep Advisor! Click here.
Thank you, Jay. It was helpful. Could you pl. tell me the algebraic route?
Well, I would not suggest you the Algebraic route; however, for the sake of your interest, here it is.

Say a = √x and b = √y

Thus,
[√{x + y - 2√(xy)} + √{x + y + 2√(xy)}] = [√{a^2 + b^2 - 2ab} + √{a^2 + b^2 + 2ab}]

= {√(a - b)^2} + {√(a + b)^2};

Since y > x, √y > √x, or b > a.

Thus, {√(a - b)^2} + {√(a + b)^2} = (b - a) + (b + a) = 2b = 2√y.

The correct answer: E

Hope this helps!

Relevant book: Manhattan Review GMAT Math Essentials Guide

-Jay
_________________
Manhattan Review GMAT Prep

Locations: New York | Mumbai | Ho Chi Minh City | Budapest | and many more...

Schedule your free consultation with an experienced GMAT Prep Advisor! Click here.
Join the discussion