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PS Question

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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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..!!!
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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
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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
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