Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 02 Sep 2015, 16:06

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# gmatclub test question M18, Q39 : ST

Author Message
Senior Manager
Joined: 06 Jul 2007
Posts: 286
Followers: 3

Kudos [?]: 44 [0], given: 0

gmatclub test question M18, Q39 : ST [#permalink]  19 Mar 2009, 02:37
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

If S and T are non-zero numbers and $$\frac{1}{S} + \frac{1}{T} = S + T$$ , which of the following is necessarily true?

A) $$ST = 1$$
B) $$S + T = 1$$
C) $$\frac{1}{S} = T$$
D) $$\frac{S}{T} = 1$$
E) none of the above
GMAT Tutor
Joined: 24 Jun 2008
Posts: 1180
Followers: 321

Kudos [?]: 1013 [0], given: 4

Re: gmatclub test question M18, Q39 : ST [#permalink]  19 Mar 2009, 04:26
Expert's post
We can find a common denominator on the left side:

$$\frac{1}{S} + \frac{1}{T} = S + T \\ \frac{T}{ST} + \frac{S}{ST} = S+T \\ \frac{S + T}{ST} = S + T$$

Now, if $$S + T \neq 0$$, we can divide both sides by $$S + T$$ to get:

$$\frac{1}{ST} = 1 \\ ST = 1$$

So if $$S + T \neq 0$$, then $$ST = 1$$ must be true. However, we can't be sure that $$S + T \neq 0$$ is true, as you can see by plugging in, say, S = 2 and T = -2. So the answer is E.
_________________

GMAT Tutor in Toronto

If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com

Re: gmatclub test question M18, Q39 : ST   [#permalink] 19 Mar 2009, 04:26
Display posts from previous: Sort by