x/y = 2/5

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

Redeem

This topic has expert replies

Post new topic Post Reply

Previous Topic Next Topic

sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 am; Location: India; Thanked: 267 times; Followed by:80 members; GMAT Score:760

x/y = 2/5

by sanju09 » Wed Sep 15, 2010 1:20 am

If x/y = 2/5, then which of the following must be true?

I. y + x = 7.
II. (x + y)/x = 7/2.
III. y^2/x^2 = 25/4.

(A) I only
(B) I and II only
(C) I and III only
(D) II and III only
(E) I, II and III

[spoiler]Source: https://readyforgmat.com[/spoiler]

The mind is everything. What you think you become. -Lord Buddha

Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com

Quote

Source: Beat The GMAT — Problem Solving | Wed Sep 15, 2010 1:20 am

limestone: Master | Next Rank: 500 Posts; Posts: 307; Joined: Sun Jul 11, 2010 7:52 pm; Thanked: 36 times; Followed by:1 members; GMAT Score:640

by limestone » Wed Sep 15, 2010 1:32 am

first, x/y = 2/5 it means y/x = 5/2

I. x + y = 7 just true only when x = 2, y =5, what if x =4, y = 10? or x = a*2, y = a*5 ( a is not 1) => not a "must-be"

II. (x+y)/x = x/x + y/x = 1 + 5/2 = 7/2, so this is a "must-be"

III. y/x = 5/2, hence (y/x)^2 = (5/2)^2, or y^2/x^2 = 5^2/2^2 = 25/4, another "must-be".

IMO, the answer is D.
Thanks sanju09 for this question.

Quote

blaster: Master | Next Rank: 500 Posts; Posts: 233; Joined: Mon Jun 09, 2008 1:30 am; Thanked: 5 times

by blaster » Wed Sep 15, 2010 1:58 am

quick ans.

x/y = 2/5

here x can be 2 or 4 , y can be 5 or 10
now statement I
y + x = 7

as we see from the statement here ans can be both 7 or other figure,let's say 4+10.
that's why stament I don't have 1 answer.

eliminate I from ans choices , only D remains.

Quote

GMAT/MBA Expert

Scott@TargetTestPrep: GMAT Instructor; Posts: 8086; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Thu Jan 18, 2018 1:32 pm

sanju09 wrote:If x/y = 2/5, then which of the following must be true?

I. y + x = 7.
II. (x + y)/x = 7/2.
III. y^2/x^2 = 25/4.

(A) I only
(B) I and II only
(C) I and III only
(D) II and III only
(E) I, II and III

We are given that x/y = 2/5, and need to determine what must be true.

I. y + x = 7

This is not true. If x = 2 and y = 5, then x + y = 7; however, if x = 4, and y = 10, then x + y does not equal 7.

(Notice that x and y do not have to equal 2 and 5, respectively; if they were to equal 4 and 10, respectively, the fraction x/y would would equal 4/10, which would reduce to 2/5.)

II. (x + y)/x = 7/2

This is true since:

(x + y)/x = x/x + y/x = 1 + 5/2 = 7/2

(Notice that if x/y = 2/5, then y/x = 5/2.)

III. y^2/x^2 = 25/4

This is true. Recall that in II, we've mentioned y/x = 5/2. Thus, y^2/x^2 = (y/x)^2 = (5/2)^2 = 25/4,

Answer: D

Scott Woodbury-Stewart
Founder and CEO
[email protected]