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# GMAT Diagnostic Test Question 5

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Re: GMAT Diagnostic Test Question 5 [#permalink]

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15 Feb 2012, 21:44
on gmat are answers displayed by increasing value?
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Re: GMAT Diagnostic Test Question 5 [#permalink]

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16 Feb 2012, 03:50
Expert's post
shawndx wrote:
on gmat are answers displayed by increasing value?

Usually the answer choices in PS are in increasing or decreasing order. But not always, and certainly not for a question such as this one where we should find the greatest value.
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Re: GMAT Diagnostic Test Question 5 [#permalink]

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03 Apr 2012, 21:34
how did you get from 2^24 to 2^4 * 10^6?
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Re: GMAT Diagnostic Test Question 5 [#permalink]

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04 Apr 2012, 01:45
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Expert's post
catty2004 wrote:
how did you get from 2^24 to 2^4 * 10^6?

$$2^{24} =2^4*2^{20}=2^4*(2^{10})^2$$. Now, since $$2^{10}=1024\approx 10^3$$ then $$2^4*(2^{10})^3\approx{2^2*(10^3)^2}=2^4 * 10^6$$.

Hope it's clear.
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Re: GMAT Diagnostic Test Question 5 [#permalink]

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10 Jun 2012, 23:11
Hi, I'm new to the forum and currently prepping for the GMAT.

For this problem I manipulated all the answers in a similar way but I wanted to focus on the two answer choices that I was left with. I actually manipulated the answer choice D in a different manner and wanted to see if the method was okay. The bold is what I'm speaking about.

A - 999^12 -> 1000^12 -> (10^3)^12 -> 10^36

and

D - (-20)^24 -> ((-2)^24)*(10^24)..here is where I did it differently -> (((-2)^3)^8)*(10^24), which then becomes ((-8)^8)*(10^24).

From here I rounded down (-8)^8 to (-10)^8 and then dropped the negative sign because it becomes positive due to the even power.
My answer then looked like this: (10^8)*(10^24) -> 10^(8+24) = 10^32

From here, 10^36 > 10^32, therefore the answer is A.
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Re: GMAT Diagnostic Test Question 5 [#permalink]

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20 Jun 2012, 09:56
Ok..i kinda get the concept.

So, can I safely assume that 2^3==10 and so, 2^24==10^3 and then discard D?

And, can we use this form for other questions as well? Ofcourse, in PS questions only (strictly speaking)
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GMAT Diagnostic Test Question 5 [#permalink]

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20 Jun 2014, 03:49
I am not sure how many of you might find this useful..but for Asian students familiar with log function...it might help

A. 999^12= 10^36=> 36 log 10 =>36

D. 20^24= As 20 is less than 3^3..thus 20^24 < 27^24 => 3^42 => 42 log 3 => 42 x 0.47 = Approx. 20

E. 15^20 < 2 ^80 => 80 log 2 = 80 x 0.3 = 24

Log values have a direct correlation with numerical value of the number...
I had learnt the values of log 3= .4771 and log 2= 0.3010 in my school days... surprisingly I was able to accurately retrieve these from my memory slot
Additionally log 1 = 0, log 10 = 1, log 100 = 2...(I guess)

I would be glad if Bunuel or Karishma validate my approach...Just to make things more clear
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GMAT Diagnostic Test Question 5   [#permalink] 20 Jun 2014, 03:49

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# GMAT Diagnostic Test Question 5

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