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The catch here is the pattern is repetitive . That makes 10000*0.00121212 (in repetitive pattern ) - 100*0.00121212 That will give you 12.121212 - 0.121212 = 12 Answer is E

The way you tried to solved it should give (10000-100 ) * 0.00121212 = 9900*0.00121212 = 11.99 edit : However It is not the best approach to solve such problem ., mostly because multiplication will take more time . E is right choice so your answer is write since there is no other answer which is near than 12 . ( I don't know why you divided it by 9999 )
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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)? <<<<<Above "12" there is a line indicates that it repeats indefinitely. However i cannot find how i can put it there

a) 0 b) 0,12(has infinite line above 12) c)1,2 d)10 e)12

Above "12" there is a line indicates that it is repeats indeinitely. However i cannot find how i will put it there

Anyway My approach is;

9900*12/9999 = 11,88 so i chose E

is there anyway ? i did right but dont know the logic under it

What is the value of \((10^4-10^2)*0.00(12)\)? (You can indicate repeated part of the decimal by putting it in brackets)

You can solve it as Pinali suggests above, just open the brackets and multiply: \((10^4-10^2)*0.00(12)=10,000*0.00(12)-100*0.00(12)=12.(12)-0.(12)=12\), you can see that 0.(12) part is subtracted from 12.(12) which gives 12.

But you can do this problem in another way too: 0.00(12) can be written as fraction \(\frac{12}{9,900}\) (as many 9's as numbers in repeated pattern and as many zeros after as zeros after decimal point). For more on how to convert a recurring decimal to fraction see Number Theory chapter of Math Book (link in my signature).

So \((10^4-10^2)*0.00(12)=9,900*\frac{12}{9,900}=12\).

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)? <<<<<Above "12" there is a line indicates that it repeats indefinitely. However i cannot find how i can put it there

a) 0 b) 0,12(has infinite line above 12) c)1,2 d)10 e)12

Above "12" there is a line indicates that it is repeats indeinitely. However i cannot find how i will put it there

Anyway My approach is;

9900*12/9999 = 11,88 so i chose E

is there anyway ? i did right but dont know the logic under it

What is the value of \((10^4-10^2)*0.00(12)\)? (You can indicate repeated part of the decimal by putting it in brackets)

You can solve it as Pinali suggests above, just open the brackets and multiply: \((10^4-10^2)*0.00(12)=10,000*0.00(12)-100*0.00(12)=12.(12)-0.(12)=12\), you can see that 0.(12) part is subtracted from 12.(12) which gives 12.

But you can do this problem in another way too: 0.00(12) can be written as fraction \(\frac{12}{9,900}\) (as many 9's as numbers in repeated pattern and as many zeros after as zeros after decimal point). For more on how to convert a recurring decimal to fraction see Number Theory chapter of Math Book (link in my signature).

So \((10^4-10^2)*0.00(12)=9,900*\frac{12}{9,900}=12\).

Answer: E.

Hope it help.s.

Thanks for explaining this and for link too ! you rock
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The catch here is the pattern is repetitive . That makes 10000*0.00121212 (in repetitive pattern ) - 100*0.00121212 That will give you 12.121212 - 0.121212 = 12 Answer is E

The way you tried to solved it should give (10000-100 ) * 0.00121212 = 9900*0.00121212 = 11.99 edit : However It is not the best approach to solve such problem ., mostly because multiplication will take more time . E is right choice so your answer is write since there is no other answer which is near than 12 . ( I don't know why you divided it by 9999 )

It is poped up in my mind, i was barely remember the rule and divide 9999 however the rule,bunuel mentioned,is we have to put 9 as much as number in the decimal different from 0.

I was trying to do that with bunuels second approach.

Thanks your way is more fast.

you got kudos from me and thanks Bunuel you are the best mate
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Re: Spent hours studying this powers problem! [#permalink]

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01 Mar 2011, 21:16

Sorry, this was my first post, not familiar with rules. Thanks for the clarity - I would never have considered factoring out that 10^2. Did you do that all in 2 minutes? Seems like it would take too long

Status: Impossible is not a fact. It's an opinion. It's a dare. Impossible is nothing.

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Re: Spent hours studying this powers problem! [#permalink]

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01 Mar 2011, 22:19

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Hey von Unless you are running a competition against a number crunching super machine. 10^2 can be ignored when compared to 10^4. Since its 1 percent. Knocking 10^2 off. 10^4 * 0.0012 = 12 approx But remember use inequality for safety - 11.9< answer < 12.0 if the choices are close.

von wrote:

Sorry, this was my first post, not familiar with rules. Thanks for the clarity - I would never have considered factoring out that 10^2. Did you do that all in 2 minutes? Seems like it would take too long

Re: A bar over a sequence of digits in a decimal indicates that [#permalink]

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03 Oct 2015, 04:50

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(10^4 - 10 ^2) (.00(12)) --- 12 within () is recurring decimal . =10^2(10^2 -1) (.00(12)) =10^2 x 99 x .00(12) =.(12) x 99 (Since 12/99 = .121212..... ) = 12

Answer E

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Re: A bar over a sequence of digits in a decimal indicates that [#permalink]

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03 May 2016, 22:49

thompstc wrote:

this might seem like a silly thing to ask about, but i need some help with my thought process on this one:

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)(0.00121212121212..)

A) 0 B) 0.12 repeating C) 1.2 D) 10 E) 12

I understand you're supposed to use the distributive property, but i'm not sure why? Following order of operations, shouldn't you simplify the parentheses first?

Hi thompstc,

You can solve this question either way. Just that by distribution, we can arrive at the answer easily. (10^4−10^2)∗0.0012 = 9,900 * (12/9,900) = 12

Re: A bar over a sequence of digits in a decimal indicates that [#permalink]

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01 Apr 2017, 05:22

(10^4-10^2)(0.00(12)) [ (12) is the repeating number] =10^2(10^2-1)(0.00(12)) =10^2(99)(0.00(12))

Let's just handle 0.00(12) Converting it to a fraction Let x= 0.00(12) 100x=0.(12) .........eq.1 (100 because we have to move the non-repeating part i.e.00 to the left of the decimal point. So two non- repeating digits, 100. If one digit, then 10 and so on.)

10000x= 12.(12) ..........eq.2 (Same logic as above. We already had 100 as we moved 00 to the left of the decimal point. Now we have to move 12 also to the left of the decimal point.)

Now eq.2 -eq. 1

9900x=12 x=12/9900 (Don't solve)

Now putting it back in the original equation given in the question

We get: 10^2*99*12/9900 =12
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A bar over a sequence of digits in a decimal indicates that [#permalink]

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13 Jun 2017, 23:26

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fatihaysu wrote:

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)?

(A) 0 (B) 0.12 (C) 1.2 (D) 10 (E) 12

Note : Rule to convert mixed recurring decimal to fraction : In the numerator write the entire given number formed by the (recurring and non - recurring parts) and subtract from it the part of the decimal that is not recurring. In the denominator, write as many nines as the number of digits recurring and then place next to it as many zeros as there are digits without recurring in the given decimal.

Converting the mixed recurring decimal (0.0012) to fraction we get; \(\frac{(12 - 00)}{9900} = \frac{12}{9900} = \frac{4}{3300}\)

(\(10^4\) -\(10^2\))(0.0012) can be written as = \((10^4 -10^2)* \frac{4}{3300}\) \(10^2(10^2 - 1)* \frac{4}{3300}\)= \(100 * (100 - 1)* \frac{4}{3300}\) \(99 * \frac{4}{33}\) \(= 3 * 4 = 12\). Answer E...

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