M7MBA wrote: ↑Sun May 10, 2020 11:21 am
If \(rs \neq 0,\) is \(\dfrac{1}{r} + \dfrac{1}{s} = 4 ?\)
(1) \(r + s = 4rs\)
(2) \(r = s\)
[spoiler]OA=A[/spoiler]
Source: Official Guide
Target question: Is 1/r + 1/s = 4?
This one is a great candidate for rephrasing the target question.
Aside: We have a free video with tips on rephrasing the target question: https://www.gmatprepnow.com/module/gmat- ... cy?id=1100
Let's add 1/r + 1/s to create ONE rational expression.
Find common denominator: s/rs + r/rs
Add numerators: (s+r)/rs
So, 1/r + 1/s = (s+r)/rs
So, rather than ask "
Does 1/r + 1/s = 4?" we can ask "
Does (s+r)/rs = 4?"
Even better, we can cross multiply the equation to get...
REPHRASED target question: Does s+r = 4sr?"
Statement 1: r + s = 4rs
This is
exactly what our REPHRASED target questions asks.
Since we can answer the
target question with certainty, statement 1 is SUFFICIENT
Statement 2: r = s
Knowing that r=s does not help us determine whether s+r = 4sr
Since we cannot answer the
target question with certainty, statement 2 is NOT SUFFICIENT
Answer: A
Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
