Find all School-related info fast with the new School-Specific MBA Forum

It is currently 23 Oct 2014, 12:57

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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

OG 11- Quant Sample- Question 15

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Senior Manager
Senior Manager
User avatar
Joined: 25 Nov 2006
Posts: 337
Schools: St Gallen, Cambridge, HEC Montreal
Followers: 2

Kudos [?]: 28 [0], given: 0

OG 11- Quant Sample- Question 15 [#permalink] New post 19 Mar 2007, 16:40
Hello,

Can someone help me with this?

"The product of all the prime numbers less than 20 is closest to which of the following powers of 10?"

The answer is:
2x3x5x7x11x13x17x19 = 9,699,690

Is there another way than multiplying manually?

Ludo
Senior Manager
Senior Manager
avatar
Joined: 29 Jan 2007
Posts: 451
Location: Earth
Followers: 2

Kudos [?]: 38 [0], given: 0

 [#permalink] New post 19 Mar 2007, 16:51
I would club them together so that each term is close to 10

like this

2 * 3 * 5 * 7 * 11 * 13 * 17 * 19 <=>

(2*5) * (3*7) * 11 * 13 * 17 * 19 <=>

10 * 21 * 11 * 13 * (17 * 19 ) <=>

10 * ( 10 * 2 ) * 11 * 13 * ( 400 ) <=> [( 17 * 19 ~ 20 * 20) ]

10 * 10 * 11 * 13 * (10 * 10 * 4) * 2 <=>

10 * 10 * 11 * 13 * (10 * 10 ) * (4 * 2 ) <=>

10 * 10 * 11 * 13 * (10 * 10 ) * (8) <=>

10 * 10 * 11 * 13 * (10 * 10 ) * (10)

which is close to 10^7

Sorry I was lazy earlier to type too much...hope this clarifies it a little bit better.

Last edited by kyatin on 19 Mar 2007, 19:02, edited 1 time in total.
Manager
Manager
avatar
Joined: 03 Mar 2007
Posts: 166
Followers: 1

Kudos [?]: 9 [0], given: 0

 [#permalink] New post 19 Mar 2007, 18:47
Sorry I am still not understanding, can you explain how you got that?

I can't believe the book explanation actually expects all to multiply all those numbers together :-D
Manager
Manager
avatar
Joined: 11 Mar 2007
Posts: 69
Followers: 1

Kudos [?]: 2 [0], given: 0

 [#permalink] New post 19 Mar 2007, 19:05
2x5=10
3x7~20 or 2x10^1
11 is approximately 10

so far we have...2x10^3 (1)

13 is approximately 15...19 is approximately 20
20x15=300=3x10^2 (2)

multiplying (1) & (2), we have 6x10^5

the only number left is 17...17x6x10^5~102x10^5~10^2x10^5~10^7
Manager
Manager
User avatar
Joined: 02 Jan 2007
Posts: 211
Followers: 2

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

 [#permalink] New post 21 Mar 2007, 10:56
I got this one wrong too when I took the Diagnostic test in the OG.



I tried the following partial solution

2 * 3 * 5 * 7 * 11 * 13 * 17 * 19

10 * 21 * 11 * 13 * 17 * 19

10 * (10*2.1) * (10*1.1) * (10* 1.3) * (10*1.7) * (10*1.9)

A total of 6 10's so it must be at least 10^6
Manager
Manager
User avatar
Joined: 02 Jan 2007
Posts: 211
Followers: 2

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

 [#permalink] New post 22 Mar 2007, 05:45
Sorry about my crazy post y'day - I have edited it now.
I checked the OA and it is 10^7.


To add to my incomplete solution above, we now have

10^6 * (2.1 * 1.1 * 1.3 * 1.7 *1.9)

Approximating,

10^6 * (2 * 1 * 1.5 * 1.5 * 2)
10^6 * ( 4 * 2.25 ) = 10^6 * (9) ~ 10^6*10

or 10^7
Manager
Manager
avatar
Joined: 15 Dec 2005
Posts: 60
Followers: 1

Kudos [?]: 2 [0], given: 0

 [#permalink] New post 22 Mar 2007, 07:06
The numbers are
2,3,5,7,11,13,17,19

Pair 2*19= 38 = 3.8 * 10
17*3= 5.1 *10
13*5=6.5 * 10
11*7= 7.7 * 10

So Powers of 10 = 4 + (4*5*7*8)=4+(2*10,5.6*10)..here I approx 3.8==> 4
=6+( 1)= 7....
  [#permalink] 22 Mar 2007, 07:06
    Similar topics Author Replies Last post
Similar
Topics:
2 Question on OG11 that are not on OG12 lamanxa 1 03 Feb 2012, 13:59
Quant: MGMAT vs. OG11 Omne 2 17 Jun 2008, 17:42
OG 11 quant/verbal review sonibubu 4 01 Sep 2007, 11:16
OG 11- Quant Sample- Question 11 lumone 6 19 Mar 2007, 16:10
OG 11 question guide baer 2 02 Sep 2006, 20:55
Display posts from previous: Sort by

OG 11- Quant Sample- Question 15

  Question banks Downloads My Bookmarks Reviews Important topics  


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

Powered by phpBB © phpBB Group and phpBB SEO

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®.