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Algebra

This topic has 4 expert replies and 1 member reply
John fran kennedi Junior | Next Rank: 30 Posts
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Algebra

Post Wed Mar 09, 2016 10:25 am
ttp://postimg.org/image/sdeoji3mf/" target="_blank">


Hello guys, I have just practiced the GMAT, as we can see on this image , I get confused to solve this. I have seen the answer explanation , but I don't understand well. I don't know whether because I don't get the question well or not.
In the answer explanation ( OG 2016) page 245, it states
=10,000(0.0012)-100(0.0012)
=12,12 - 0,12

I don't know why it's 12,12, not 12.

I do need your help to make me understand. Thanks in advance

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Post Mon Oct 09, 2017 7:33 am
A common mistake that students make on a problem like this is to subtract the exponents. But of course we cannot subtract the exponents when we're subtracting terms with the same base.

More on this here: http://www.beatthegmat.com/fdp-problem-og-ps-174-t288679.html#763953

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Matt@VeritasPrep GMAT Instructor
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Post Thu Mar 17, 2016 9:26 pm
Another idea here: since (xy/99) = .xyxyxyxy..., we can say that

.0012121212... =

.12121212... * (1/100) =

12/99 * 1/100 =

12/9900

Now we have

(10⁴ - 10²) * 12/9900 =

9900 * 12/9900 =

12

and we're set!

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John fran kennedi Junior | Next Rank: 30 Posts
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Post Wed Mar 09, 2016 10:47 am
Wow, I really do understand now. Thank you so much

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Post Wed Mar 09, 2016 10:35 am
Quote:
A bar over a sequence of digits in a decimal indicates that the sequence repeats indefinitely. What is the value of (10^4 - 10^2) (0.0012)?

Note: There is a bar over "12" in 0.0012.

(A) 0
(B) 0.12 (with the bar over the 12)
(C) 1.2
(D) 10
(E) 12
We can also apply some number sense here.

(10⁴ - 10²)(0.00121212...) = (10,000 - 100)(0.00121212...)
= 9900(0.00121212...)
= (a bit less than 10,000)(0.00121212...)

Well, (10,000)(0.00121212...) = 12.121212
So, (a bit less than 10,000)(0.00121212...) = a bit less than 12.121212...

Check the answer choices:
A) 0
B) 0.121212...
C) 1.2
D) 10
E) 12

E is the best match

Cheers,
Brent

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Post Wed Mar 09, 2016 10:34 am
Quote:
A bar over a sequence of digits in a decimal indicates that the sequence repeats indefinitely. What is the value of (10^4 - 10^2) (0.0012)?

Note: There is a bar over "12" in 0.0012.

(A) 0
(B) 0.12 (with the bar over the 12)
(C) 1.2
(D) 10
(E) 12
(10⁴ - 10²)(0.00121212...) = 10⁴(0.00121212...) - 10²(0.00121212...)
= 12.121212... - 0.121212...
= 12 (since the decimal parts, in blue, are identical, they cancel out]

Answer: E

Cheers,
Brent

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