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Prime Factor

This topic has 2 expert replies and 1 member reply
candygal79 Senior | Next Rank: 100 Posts
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Prime Factor

Post Fri Apr 04, 2014 12:22 am
What is the sum of different positive Prime Factor of 550 ?

A 10

B 11

C 15

D 16

E 18

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Abhishek009 Master | Next Rank: 500 Posts
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Top Reply
Post Sat Apr 05, 2014 7:12 am
candygal79 wrote:
What is the sum of different positive Prime Factor of 550 ?

A 10

B 11

C 15

D 16

E 18
Find the factors of 550

550 = 5^2 X 2 X 11

Now we are required to find only the sum of different positive Prime Factor of the number , so the sum is -

5 + 2 + 11 => 18

_________________
Abhishek

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Post Fri Apr 04, 2014 1:29 pm
Hi candygal79,

There's a math rule called 'prime factorization' that you might occasionally use on the GMAT. The idea is that any positive number can be "broken down" into a bunch of prime numbers that are multiplied together (unless the number is already prime).

eg 10 = 2x5

Here, we're asked to prime factor 550; this can be done in a set of steps.

550 = 55x10

55 = 5x11
10 = 2x5

So 550 = 2x5x5x11

GMAT assassins aren't born, they're made,
Rich

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Contact Rich at Rich.C@empowergmat.com

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Abhishek009 Master | Next Rank: 500 Posts
Joined
11 Mar 2009
Posted:
357 messages
Followed by:
2 members
Upvotes:
50
Target GMAT Score:
900+
Post Sat Apr 05, 2014 7:12 am
candygal79 wrote:
What is the sum of different positive Prime Factor of 550 ?

A 10

B 11

C 15

D 16

E 18
Find the factors of 550

550 = 5^2 X 2 X 11

Now we are required to find only the sum of different positive Prime Factor of the number , so the sum is -

5 + 2 + 11 => 18

_________________
Abhishek

  • +1 Upvote Post
  • Quote
  • Flag

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