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# GMATPrep PS Questions - Need Help

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Intern
Joined: 08 Apr 2010
Posts: 22
GMATPrep PS Questions - Need Help [#permalink]

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09 May 2010, 14:10
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Math Expert
Joined: 02 Sep 2009
Posts: 46305
Re: GMATPrep PS Questions - Need Help [#permalink]

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09 May 2010, 14:26
1
1
If $$n$$ is multiple of $$5$$, and $$n = p^2q$$ where $$p$$ and $$q$$ are prime, which of the following must be a multiple of $$25$$?

A $$p^2$$
B. $$q^2$$
C. $$pq$$
D. $$p^2q^2$$
E. $$p^3q$$

$$n=5k$$ and $$n=p^2p$$, ($$p$$ and $$q$$ are primes).
Q: $$25m=?$$

Well obviously either $$p$$ or $$q$$ is $$5$$. As we are asked to determine which choice MUST be multiple of $$25$$, right answer choice must have BOTH, $$p$$ and $$q$$ in power of 2 or higher to guarantee the divisibility by $$25$$. Only D offers this.

If d is the standard deviation x,y,and z, what is the standard deviation of x+5, y+5, z+5

A. d
B. 3d
C. 15d
D. d+5
E. d+15

TIP:
If we add or subtract a constant to each term in a set:
Mean will increase or decrease by the same constant.
SD will not change.

If we increase or decrease each term in a set by the same percent (multiply by a constant):
Mean will increase or decrease by the same percent.
SD will increase or decrease by the same percent.

So in our case SD won't change as we are adding 5 to each term in a set --> SD=d.

More about standard deviation:
math-standard-deviation-87905.html

Hope it helps.

P.S. Pleas post one question per topic.
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Posts: 7066
Re: GMATPrep PS Questions - Need Help [#permalink]

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18 Sep 2017, 08:23
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--== Message from GMAT Club Team ==--

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If you would like to discuss this question please re-post it in the respective forum. Thank you!

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_________________
Re: GMATPrep PS Questions - Need Help   [#permalink] 18 Sep 2017, 08:23
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# GMATPrep PS Questions - Need Help

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