If rs does not = 0, is 1/r + 1/s = 4
S1. r + s = 4rs
S2. r = s
My issue here is with statement two...
if r = s then why can i not insert this into the equation in the stem and re write as 1/r + 1/r = 4 solve for r and be done with it?
on other problems i have seen where they say x = y and you can take that info back to the stem and turn X*Y into X^2.. but here that doesnt apply...damn you gmat...
quant review problem 124
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The question is asking whether (1/r + 1/s) = 4 or not.HPengineer wrote:If rs does not = 0, is 1/r + 1/s = 4
S1. r + s = 4rs
S2. r = s
My issue here is with statement two...
if r = s then why can i not insert this into the equation in the stem and re write as 1/r + 1/r = 4 solve for r and be done with it?
If you replace r = s from the statement 2 into the equation, obviously you'll get a value of r which satisfies the equation. The solutions are in fact r = s = 1/2. But the question is not really asking you to do this! For this particular set of values of r and s the relation satisfies. But not for all r and s that satisfies the relation r = s. For instance, r = s = 1 does not satisfies the equation. Thus statement 2 is not sufficient to answer the question.
But for statement 1, (r + s) = 4rs => (r + s)/rs = 4 => (1/r + 1/s) = 4.
Therefore for any set of values of r and s that satisfies the condition given in statement 1, satisfies the equation given in question stem. Hence statement 1 is sufficient.
Hope that clears your confusion.
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in short, as anurag said statement 2 is only true at one value r=s=1/2.
it is false for every other value, hence insufficient,
u need to have an equation satisfy any given set of values for a statement to be sufficient
it is false for every other value, hence insufficient,
u need to have an equation satisfy any given set of values for a statement to be sufficient
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Quant 47-Striving for 50
Verbal 34-Striving for 40
My gmat journey :
https://www.beatthegmat.com/710-bblast-s ... 90735.html
My take on the GMAT RC :
https://www.beatthegmat.com/ways-to-bbla ... 90808.html
How to prepare before your MBA:
https://www.youtube.com/watch?v=upz46D7 ... TWBZF14TKW_