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

It is currently 26 Oct 2014, 00:53

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

Multiplication the only way?

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Intern
Intern
User avatar
Status: What to know what someone's dream looks like? Observe a large pile of GMAT books. (c)
Joined: 30 Sep 2010
Posts: 28
Followers: 0

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

GMAT ToolKit User
Multiplication the only way? [#permalink] New post 14 Dec 2010, 17:18
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

50% (00:00) correct 50% (00:27) wrong based on 2 sessions
The product of all prime numbers less than 20 is closest to which of the following powers of 10?

A) 10^9
B) 10^8
C) 10^7
D) 10^6
E) 10^5

Image Posted from GMAT ToolKit
[Reveal] Spoiler: OA
Kaplan Promo CodeKnewton GMAT Discount CodesManhattan GMAT Discount Codes
Director
Director
User avatar
Joined: 03 Sep 2006
Posts: 889
Followers: 6

Kudos [?]: 171 [0], given: 33

Re: Multiplication the only way? [#permalink] New post 14 Dec 2010, 18:57
2*3*5*7*11*13*17*19

quick calculation:

3*10*77*13*17*19

231*10*13*17*19

231*10*221*19

231*221*190

Above steps did not take me much time, but after this I think one needs to be strong in multiplication!

If there is some short cut, it would be great to know....but I won't take the risk of some short cut which might result in wrong answer during the exam.

51051*190

=9699690

closer to 100,00000

which means 10^7
Expert Post
Veritas Prep GMAT Instructor
User avatar
Joined: 16 Oct 2010
Posts: 4877
Location: Pune, India
Followers: 1157

Kudos [?]: 5385 [0], given: 165

Re: Multiplication the only way? [#permalink] New post 14 Dec 2010, 19:15
Expert's post
My response from another thread:

Quickly approximate
2, 3, 5, 7, 11, 13, 17, 19
Make groups
2*5 = 10
3*17 = 50 (approximately)
7*13 = 100 (approximately)
11*19 = 200 (approximately)
So you make 7 zeroes (the 2 and the 5 also make a 0). When you multiply all these, the answer will be close to 10^7
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Save $100 on Veritas Prep GMAT Courses And Admissions Consulting
Enroll now. Pay later. Take advantage of Veritas Prep's flexible payment plan options.

Veritas Prep Reviews

Intern
Intern
avatar
Joined: 15 Nov 2010
Posts: 20
Followers: 0

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

Re: Multiplication the only way? [#permalink] New post 15 Dec 2010, 05:50
"My response from another thread:

Quickly approximate
2, 3, 5, 7, 11, 13, 17, 19
Make groups
2*5 = 10
3*17 = 50 (approximately)
7*13 = 100 (approximately)
11*19 = 200 (approximately)
So you make 7 zeroes (the 2 and the 5 also make a 0). When you multiply all these, the answer will be close to 10^7 "

Dear Karishma, a quick question on this:
when i actually multiply the numbers, i get 10^6..there are only 6 zeros from what I see. What am I overlooking ?
Thank you in advance!
Expert Post
Veritas Prep GMAT Instructor
User avatar
Joined: 16 Oct 2010
Posts: 4877
Location: Pune, India
Followers: 1157

Kudos [?]: 5385 [0], given: 165

Re: Multiplication the only way? [#permalink] New post 15 Dec 2010, 06:05
Expert's post
0987654312 wrote:
"My response from another thread:

Quickly approximate
2, 3, 5, 7, 11, 13, 17, 19
Make groups
2*5 = 10
3*17 = 50 (approximately)
7*13 = 100 (approximately)
11*19 = 200 (approximately)
So you make 7 zeroes (the 2 and the 5 also make a 0). When you multiply all these, the answer will be close to 10^7 "

Dear Karishma, a quick question on this:
when i actually multiply the numbers, i get 10^6..there are only 6 zeros from what I see. What am I overlooking ?
Thank you in advance!


The 5 of 50 and the 2 of 200 above multiply to make another 0.
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Save $100 on Veritas Prep GMAT Courses And Admissions Consulting
Enroll now. Pay later. Take advantage of Veritas Prep's flexible payment plan options.

Veritas Prep Reviews

Re: Multiplication the only way?   [#permalink] 15 Dec 2010, 06:05
    Similar topics Author Replies Last post
Similar
Topics:
4 Experts publish their posts in the topic Understanding questions in multiple ways - how important? DelSingh 7 06 Aug 2012, 10:49
Entry Level Currently (Only Way To Go Is UP!) MissShona 4 18 Aug 2010, 23:56
Many people think that the only way to remedy the problem of rockubabe 3 22 May 2010, 14:33
1 Experts publish their posts in the topic The only way for growers to salvage frozen citrus is to tejal777 13 31 Oct 2009, 15:02
The only way that bookstores can profitably sell books at sushmash 4 28 Apr 2009, 11:16
Display posts from previous: Sort by

Multiplication the only way?

  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®.