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# If xy = 10, what is the value of x + y?

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Re: If xy = 10, what is the value of x + y? [#permalink]
GMATPrepNow wrote:
Statement 2: 1/x + 1/y = 3
Let's combine these fractions. To do so, we'll need a common denominator.
A common denominator of x and y is xy.
So, 1/x = y/xy and 1/y = x/xy
We can now take: 1/x + 1/y = 3
And rewrite it as: y/xy + x/xy = 3
Combine the fractions: (y + x)/xy = 3
Use the given information to get: (y + x)/10 = 3
Multiply both sides by 10 to get: y + x = 30
PERFECT!
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Cheers,
Brent

Hi Bent,

IN statement 2, I did it another way and I need your view.

xy=10............(1)

1/x + 1/y = 3...(2)

Multiple both equations

xy(1/x + 1/y)=30

x+ y =30....Perfect.

Is there any restriction for above method?

Thanks
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Re: If xy = 10, what is the value of x + y? [#permalink]
Top Contributor
Mo2men wrote:
GMATPrepNow wrote:
Statement 2: 1/x + 1/y = 3
Let's combine these fractions. To do so, we'll need a common denominator.
A common denominator of x and y is xy.
So, 1/x = y/xy and 1/y = x/xy
We can now take: 1/x + 1/y = 3
And rewrite it as: y/xy + x/xy = 3
Combine the fractions: (y + x)/xy = 3
Use the given information to get: (y + x)/10 = 3
Multiply both sides by 10 to get: y + x = 30
PERFECT!
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Cheers,
Brent

Hi Bent,

IN statement 2, I did it another way and I need your view.

xy=10............(1)

1/x + 1/y = 3...(2)

Multiple both equations

xy(1/x + 1/y)=30

x+ y =30....Perfect.

Is there any restriction for above method?

Thanks

That's a perfect solution!
I don't believe there are any restrictions on this technique.

Cheers,
Brent
Re: If xy = 10, what is the value of x + y? [#permalink]
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