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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?

10
12
15
18
30

ANS is D, why???

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ri2007: Master | Next Rank: 500 Posts; Posts: 258; Joined: Mon Aug 27, 2007 12:43 pm; Thanked: 15 times

by ri2007 » Fri Nov 30, 2007 10:58 am

I did this by plugging the values

So ,

if u solve the equation in the question stem u get

10 ( x+2y) / (x+y) = k

Now just plug the value of each ans choice instead of K

you will see that the only solution where x<y and both are positive is with 18 as the ans.

Is there a better way to do this?

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