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Prime Factor

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by candygal79 » 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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by Brent@GMATPrepNow » Fri Apr 04, 2014 12:30 am
candygal79 wrote:What is the sum of different positive Prime Factor of 550 ?

A 10

B 11

C 15

D 16

E 18
550 = (2)(5)(5)(11)
So, the DIFFERENT prime factors are 2, 5 and 11
2 + 5 + 11 = [spoiler]18 = E[/spoiler]

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by [email protected] » 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

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by Abhishek009 » 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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