product of prime numbers

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product of prime numbers [#permalink]

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

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Re: product of prime numbers [#permalink]

13 Jun 2009, 00:12

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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Re: product of prime numbers [#permalink]

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

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Re: product of prime numbers [#permalink]

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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product of prime numbers

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