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Strongt: Senior | Next Rank: 100 Posts; Posts: 51; Joined: Wed Jan 05, 2011 3:32 amFollowed by: 1 member

by Strongt » Tue Apr 19, 2011 7:44 am

If w/x = 2/3 and w/y = 8/15, then (x + y)/y =

answer is [spoiler]9/5[/spoiler]

I get to the point where 3w = 2x; and 15w = 8y, then I dont get how the next step is made

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Source: Beat The GMAT — Problem Solving | Tue Apr 19, 2011 7:44 am

manpsingh87: Master | Next Rank: 500 Posts; Posts: 436; Joined: Tue Feb 08, 2011 3:07 amFollowed by: 6 members; Thanked: 72 times

by manpsingh87 » Tue Apr 19, 2011 7:58 am

Strongt wrote:If w/x = 2/3 and w/y = 8/15, then (x + y)/y =

answer is [spoiler]9/5[/spoiler]

I get to the point where 3w = 2x; and 15w = 8y, then I dont get how the next step is made

x=(3/2)w; y=(15/8)w;
x+y=(3/2)w+(15/8)w = (12+15)w/8=27w/8;
x+y/y=(27w/8)*(8/15w)=9/5..!!!

O Excellence... my search for you is on... you can be far.. but not beyond my reach!

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pemdas: Legendary Member; Posts: 1084; Joined: Fri Apr 15, 2011 2:33 pmFollowed by: 21 members; Thanked: 158 times

by pemdas » Tue Apr 19, 2011 8:05 am

w/x = 2/3 and w/y = 8/15,

then (x + y)/y = ?

let's rewrite -> w/x = 2*4/3*4 OR 8/12

now w : x : y = 8:12:15, (x + y)/y = x/y +1 OR (12/15 +1)= 4/5 + 1 = 9/5

Success doesn't come overnight!

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Ian Stewart: GMAT Instructor; Posts: 2623; Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members; Location: Montreal; Thanked: 1090 times; GMAT Score:780

by Ian Stewart » Tue Apr 19, 2011 9:14 am

Strongt wrote:If w/x = 2/3 and w/y = 8/15, then (x + y)/y =

answer is [spoiler]9/5[/spoiler]

I get to the point where 3w = 2x; and 15w = 8y, then I dont get how the next step is made

There are a number of possible approaches here. First you might notice that we only need to find the ratio of x to y to complete the question since:

(x+y)/y = (x/y) + (y/y) = (x/y) + 1

Now we can multiply the given fractions so that the w cancels and we are left with x/y. Since w/x = 2/3, it must be that x/w = 3/2. so:

(x/w)(w/y) = x/y = (3/2)(8/15) = 4/5

and (x/y) + 1 = 9/5

For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com

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