Data Sufficiency

[vrowland]

If rs is not equal to 0, is 1/r + 1/s = 4,

(1) r + s = 4rs
(2) r = s




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[student22]

Is it A?

1/r + 1/s = 4 --> rs * (1/r + 1/s = 4) --> s + r = 4s. This is the same as statement 1. So that is sufficient.

Statement 2: Let's try:

1/s + 1/s = 2/s. Not sufficient, no idea what s is.

Let me know if I'm right.

[dxgamez]

Right, A for me too.

1. s + r = 4rs, same as question, so sufficient

2. r-s = 0, if r & s are +ve fraction then ans to qn stem is true but if they are -ve fractions, then it would be false. so insufficient.

[onedayi'll]

+1 A

[[email protected]]

If rs is not equal to 0, is 1/r + 1/s = 4,
can be simplified as (r+s)/rs=4

(1) r + s = 4rs
so
(r+s)/rs=4
=>4rs/rs=4
rs is cancelled, 4=4

insufficient

(2) r = s
so
(r+s)/rs=4
=>2r/rs=4
=>2/4=s
=>s=1/2
and r=1/2

(2) is sufficient, answer is B

[[email protected]]

oops, sorry, i missed the question details

(1 ) is sufficient to determine, 1/r+1/s=4, as r+s=4rs

so answer should be D

[ssuarezo]

oops, sorry, i missed the question details

(1 ) is sufficient to determine, 1/r+1/s=4, as r+s=4rs

so answer should be D

Yes, to me it's also D, each is sufficient.
What's the OA please?

Silvia

[eaakbari]

If rs is not equal to 0, is 1/r + 1/s = 4,
can be simplified as (r+s)/rs=4

(1) r + s = 4rs
so
(r+s)/rs=4
=>4rs/rs=4
rs is cancelled, 4=4

insufficient

(2) r = s
so
(r+s)/rs=4
=>2r/rs=4
=>2/4=s
=>s=1/2
and r=1/2

(2) is sufficient, answer is B

The answer should be A.
The mistake you are making is substituting the statement into what we have to prove.
The approach should be using the statement to prove the question
We are merely given r = s
take r and s as 5
1/5+1/5 is definitely not equal to 4
So statement two is insuff

Keep one thing in mind to avoid these mistakes, that in DS questions the statements will never contradict each other, if one says that x = 2 even the other should imply that. We merely have to decide whether the information will suffice ,it will never contradict

[[email protected]]

yep, you are right, I made a mistake understanding the question

[outreach]

1/r + 1/s =r+s/rs - eq1

A)

substituting r + s = 4rs in eq1
4rs/rs=4

hence sufficient

B) substitutin r = s in eq1
2r/r^2=2/r

value of r is not known hence insuffcient

If rs is not equal to 0, is 1/r + 1/s = 4,

(1) r + s = 4rs
(2) r = s




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[Scott@TargetTestPrep]

If rs is not equal to 0, is 1/r + 1/s = 4,

(1) r + s = 4rs
(2) r = s




[/spoiler]

Solution:

Question Stem Analysis:

We need to determine whether 1/r + 1/s = 4, i.e., (r + s)/(rs) = 4.

Statement One Alone:

Since r + s = 4rs, we have (r + s)/(rs) = (4rs)/(rs) = 4. Statement one alone is sufficient.

Statement Two Alone:

Statement two is not sufficient. For example, if r = s = 1/2, 1/r + 1/s = 2 + 2 = 4. However, if r = s = 1, 1/r + 1/s = 1 + 1 = 2.

Answer: A