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Source: — Data Sufficiency |
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by ColumbiaVC » Sun Jul 24, 2011 8:19 pm
C
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by Anurag@Gurome » Sun Jul 24, 2011 8:44 pm
anujmalik wrote:What is the ratio of r to s?

(1) r + s = 7

(2) r^2 - s^2 = 7
(1) r, s can take many values so that r + s = 7, viz., r = 4, s = 3, r = 2, s = 5, r = 1, s = 6 and so on. We don't have a definite answer; NOT sufficient.

(2) r² - s² = 7 or (r + s)(r - s) = 7
Now, r = 4, s = 3 then r : s = 4 : 3
r = 4, s = -3 then r : s = 4 : -3
No definite answer; NOT sufficient.

Combining (1) and (2), the only possible value of r = 4 and s = 3, so r : s = 4 : 3

The correct answer is C.
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by anujmalik » Mon Jul 25, 2011 2:49 pm
Thanks Anurag I missed the values 4 and -3 and thus ended up with B thinking only 4 and 3 could solve this and thus A is not need but your explanation clearly shows the possible values!!
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by GAMATO » Tue Jul 26, 2011 8:35 am
Hi Anurag,

I tried to solve it in a different way and got E. Could you please help me understand where am i going wrong?

Statement(1): r + s = 7
picking numbers: r = 3, s = 4 and r = 4, s = 3 we can say that St (1) is NOT sufficient

Statement(2): r^2 - s^2 = 7
(r-s)*(r+s)= 7

Again picking numbers r = 4, s = 3 and r = 4, s = -3 we can say that St (2) is NOT sufficient

Combining (1) and (2)

(r-s)*(r+s)= 7
(r-s)*7= 7
r-s = 1

So both options together are NOT sufficient.

Am I doing something wrong?


Anurag@Gurome wrote:
anujmalik wrote:What is the ratio of r to s?

(1) r + s = 7

(2) r^2 - s^2 = 7
(1) r, s can take many values so that r + s = 7, viz., r = 4, s = 3, r = 2, s = 5, r = 1, s = 6 and so on. We don't have a definite answer; NOT sufficient.

(2) r² - s² = 7 or (r + s)(r - s) = 7
Now, r = 4, s = 3 then r : s = 4 : 3
r = 4, s = -3 then r : s = 4 : -3
No definite answer; NOT sufficient.

Combining (1) and (2), the only possible value of r = 4 and s = 3, so r : s = 4 : 3

The correct answer is C.
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by nkumar13 » Tue Jul 26, 2011 12:58 pm
I also came up with answer as E.

Anurag,
In statement 1 why are we not considering r = 8 & s = -1.
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by GAMATO » Wed Jul 27, 2011 9:52 am
Oops.. combining (1) and (2)
(r-s)*(r+s)= 7
(r-s)*7= 7
r-s = 1
Again r+s = 7
2r = 8
r = 4 and s 7-4 = 3

C is the Answer...

GAMATO wrote:Hi Anurag,

I tried to solve it in a different way and got E. Could you please help me understand where am i going wrong?

Statement(1): r + s = 7
picking numbers: r = 3, s = 4 and r = 4, s = 3 we can say that St (1) is NOT sufficient

Statement(2): r^2 - s^2 = 7
(r-s)*(r+s)= 7

Again picking numbers r = 4, s = 3 and r = 4, s = -3 we can say that St (2) is NOT sufficient

Combining (1) and (2)

(r-s)*(r+s)= 7
(r-s)*7= 7
r-s = 1

So both options together are NOT sufficient.

Am I doing something wrong?


Anurag@Gurome wrote:
anujmalik wrote:What is the ratio of r to s?

(1) r + s = 7

(2) r^2 - s^2 = 7
(1) r, s can take many values so that r + s = 7, viz., r = 4, s = 3, r = 2, s = 5, r = 1, s = 6 and so on. We don't have a definite answer; NOT sufficient.

(2) r² - s² = 7 or (r + s)(r - s) = 7
Now, r = 4, s = 3 then r : s = 4 : 3
r = 4, s = -3 then r : s = 4 : -3
No definite answer; NOT sufficient.

Combining (1) and (2), the only possible value of r = 4 and s = 3, so r : s = 4 : 3

The correct answer is C.
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by Anurag@Gurome » Wed Jul 27, 2011 6:47 pm
GAMATO wrote:Oops.. combining (1) and (2)
(r-s)*(r+s)= 7
(r-s)*7= 7
r-s = 1
Again r+s = 7
2r = 8
r = 4 and s 7-4 = 3

C is the Answer...

GAMATO wrote:Hi Anurag,

I tried to solve it in a different way and got E. Could you please help me understand where am i going wrong?

Statement(1): r + s = 7
picking numbers: r = 3, s = 4 and r = 4, s = 3 we can say that St (1) is NOT sufficient

Statement(2): r^2 - s^2 = 7
(r-s)*(r+s)= 7

Again picking numbers r = 4, s = 3 and r = 4, s = -3 we can say that St (2) is NOT sufficient

Combining (1) and (2)

(r-s)*(r+s)= 7
(r-s)*7= 7
r-s = 1

So both options together are NOT sufficient.

Am I doing something wrong?


Anurag@Gurome wrote:
anujmalik wrote:What is the ratio of r to s?

(1) r + s = 7

(2) r^2 - s^2 = 7
(1) r, s can take many values so that r + s = 7, viz., r = 4, s = 3, r = 2, s = 5, r = 1, s = 6 and so on. We don't have a definite answer; NOT sufficient.

(2) r² - s² = 7 or (r + s)(r - s) = 7
Now, r = 4, s = 3 then r : s = 4 : 3
r = 4, s = -3 then r : s = 4 : -3
No definite answer; NOT sufficient.

Combining (1) and (2), the only possible value of r = 4 and s = 3, so r : s = 4 : 3

The correct answer is C.
That's right. You answered it on your own :)
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
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