It is currently 16 Jan 2018, 13:36

Close

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
Your Progress

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If d=1/(2^3*5^7) is expressed as a terminating decimal, how

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Manager
Manager
User avatar
B
Joined: 09 Mar 2016
Posts: 133

Kudos [?]: 23 [0], given: 183

Re: If d=1/(2^3*5^7) is expressed as a terminating decimal, how [#permalink]

Show Tags

New post 31 Dec 2017, 05:12
[/quote]

Frankly, the red part does not make any sense...

The denominator is \(2^7*5^7\). Multiply it by \(2^4\). What do you get?[/quote]

Hello Bunuel, i have the same question: based on which rule are you multiplying (2^3*5^7) by 2^4 but still ignoring 5^7 ? please help me to understand your smart solution :-) and to answer your question: if multiply (2^3*5^7) by 2^4 I get 2^7 *10^11 Thanks!

Kudos [?]: 23 [0], given: 183

PS Forum Moderator
avatar
P
Joined: 25 Feb 2013
Posts: 806

Kudos [?]: 378 [0], given: 42

Location: India
GPA: 3.82
GMAT ToolKit User Premium Member Reviews Badge CAT Tests
If d=1/(2^3*5^7) is expressed as a terminating decimal, how [#permalink]

Show Tags

New post 31 Dec 2017, 07:24
1
This post was
BOOKMARKED
dave13 wrote:


Frankly, the red part does not make any sense...

The denominator is \(2^7*5^7\). Multiply it by \(2^4\). What do you get?[/quote]

Hello Bunuel, i have the same question: based on which rule are you multiplying (2^3*5^7) by 2^4 but still ignoring 5^7 ? please help me to understand your smart solution :-) and to answer your question: if multiply (2^3*5^7) by 2^4 I get 2^7 *10^11 Thanks![/quote]

Hi dave13

Properties of exponents say that if base is equal then on multiplying you add the powers and on dividing you subtract the powers

i.e. \(a^b*c^d\) if multiplied by \(a^x\), then it will become \(a^{(b+x)}*c^d\), here there will be no impact on \(c^d\) which has a different base.

In this problem as \(5^7\) has a power of \(7\) so we need to make \(2^3\) as \(2^7\), hence we multiply the numerator & denominator by \(2^4\)

so \(2^3*5^7*2^4=2^{(3+4)}*5^7=2^7*5^7=(2*5)^7=10^7\)

Kudos [?]: 378 [0], given: 42

Intern
Intern
User avatar
B
Joined: 11 Sep 2017
Posts: 15

Kudos [?]: 1 [0], given: 100

CAT Tests
Re: If d=1/(2^3*5^7) is expressed as a terminating decimal, how [#permalink]

Show Tags

New post 31 Dec 2017, 13:08
ilovefrankee wrote:
(First ever post!)

I realise I'm a little late submitting my answer here, but my answer was 2 non-zero digits: 2 & 5.

My answer is based on the following:

1 / (2^3*5^7) = 1 / (2*(2^2))*(5^7) =
1 / (4x10^7) =
25 x 10^8 .

I'm guessing my mistake was in factoring the denominator, specifically factoring of 2^3 as 2x2^2?

Any input greatly appreciated,

Ben

EDIT:

Not to worry, I've gone over some other exponent materials and came up with the correct solution.


Hi Ben,

I'd like to highlight a few things-

1. The two non zero digits are ONE and SIX and not 2 & 5.

2. In your manipulation of the expression, notice that you have missed out a TWO in the 3rd step (1 / (2*(2^2))*(5^7) =
1 / (4x10^7) and where did you get that TEN (1 / (2*(2^2))*(5^7) =
1 / (4x10^7)) from?

Correct manipulation will be: 1 / (2^3*5^7) = 1 / (2^3*5^7) * 2^4/ 2^4 = 2^4/ 10^7 = 16/ 10^7 = 0.0000016. Hence, the two non zero digits are 1 and 6.

Hope this helps.

Aiena.

Kudos [?]: 1 [0], given: 100

Manager
Manager
User avatar
B
Joined: 09 Mar 2016
Posts: 133

Kudos [?]: 23 [0], given: 183

Re: If d=1/(2^3*5^7) is expressed as a terminating decimal, how [#permalink]

Show Tags

New post 02 Jan 2018, 02:58
niks18 wrote:
dave13 wrote:


Frankly, the red part does not make any sense...

The denominator is \(2^7*5^7\). Multiply it by \(2^4\). What do you get?


Hello Bunuel, i have the same question: based on which rule are you multiplying (2^3*5^7) by 2^4 but still ignoring 5^7 ? please help me to understand your smart solution :-) and to answer your question: if multiply (2^3*5^7) by 2^4 I get 2^7 *10^11 Thanks![/quote]

Hi dave13

Properties of exponents say that if base is equal then on multiplying you add the powers and on dividing you subtract the powers

i.e. \(a^b*c^d\) if multiplied by \(a^x\), then it will become \(a^{(b+x)}*c^d\), here there will be no impact on \(c^d\) which has a different base.

In this problem as \(5^7\) has a power of \(7\) so we need to make \(2^3\) as \(2^7\), hence we multiply the numerator & denominator by \(2^4\)

so \(2^3*5^7*2^4=2^{(3+4)}*5^7=2^7*5^7=(2*5)^7=10^7\)[/quote]

Thanks a lot niks18 for a detailed explanation. Highly appreciated!

Kudos [?]: 23 [0], given: 183

Re: If d=1/(2^3*5^7) is expressed as a terminating decimal, how   [#permalink] 02 Jan 2018, 02:58

Go to page   Previous    1   2   [ 24 posts ] 

Display posts from previous: Sort by

If d=1/(2^3*5^7) is expressed as a terminating decimal, how

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.