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product of prime numbers

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Intern
Joined: 08 Jun 2009
Posts: 33
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Kudos [?]: 20 [0], given: 0

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12 Jun 2009, 21:28
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Is there any quick way to solve this question?

The product of all the 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

[Reveal] Spoiler:
OA is C
Founder
Affiliations: AS - Gold, HH-Diamond
Joined: 04 Dec 2002
Posts: 13759
Location: United States (WA)
GMAT 1: 750 Q49 V42
GPA: 3.5
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Kudos [?]: 18878 [0], given: 4237

Re: product of prime numbers [#permalink]

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13 Jun 2009, 00:12
Expert's post
Welcome to GMAT Club Jozu!

There is a neater way to post questions. You can learn how to post math symbols here: writing-mathematical-symbols-in-posts-72468.html. Usually, all you have to do is to highlight the text and hit the M button. Bu there are exceptions such as fractions.

You can also hide the Original Answer using the "Spoiler" functionality. I added it to your post. Here is the original question rewritten:

The product of all the 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) $$10^5$$
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Senior Manager
Joined: 08 Jan 2009
Posts: 329
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Kudos [?]: 119 [0], given: 5

Re: product of prime numbers [#permalink]

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13 Jun 2009, 03:26
i found this method in another forum. thought i could share it with u.

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

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

1001 * 10 * (18-1))(18+1) 3

approximately 10^4 *(324-1) *3

10^4 * 323*3

9690000

nearest power 10 is 10^7
Manager
Joined: 04 Sep 2010
Posts: 84
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Kudos [?]: 6 [0], given: 11

Re: product of prime numbers [#permalink]

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16 Jun 2011, 21:45
how to solve this question using approximation method?
Re: product of prime numbers   [#permalink] 16 Jun 2011, 21:45
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