redfield wrote:
GMATPrepNow wrote:
At 1:30 in the video
http://www.gmatprepnow.com/module/gmat- ... /video/825, we explain the process using a tree diagram. The process works for ANY number.
Cheers
Brent
So you see 14,000 and have to do a factor tree starting with a number you can eyeball like 140 and 100 then continue breaking those numbers down?
I'm sorry if I'm missing something here (feel like I'm definitely overcomplicating or simply not getting a simple idea); but when I see a number like 30,030 and one of the steps is "30,030 = 2*3*5*7*11*13" it seems like I'm missing an entire part of the explanation because it seems the speed people are getting these primes would be something more streamlined than a factor tree. It's possible it's just a matter of practice makes it faster I just wasn't sure if I was missing an entire step.
Thank you for the explanations.
Start with 30,030
I can see this is divisible by 10.
So, 30,030 = (3003)(10)
Or 30,030 = (3003)(2)(5)
What about 3003?
Well, the sum of the digits is 6, and 6 is divisible by 3, which means 3003 is divisible by 3 (this in an important divisibility rule that's discussed in this free video:
http://www.gmatprepnow.com/module/gmat- ... /video/822 )
So, 30,030 = (3)(1001)(2)(5)
This is where it gets a bit tricky since it's hard to see any PRIME divisors of 1001. We know that 2, 3 and 5 don't work. What about 7?
When we check we get: 1001 = (7)(143)
So, 30,030 = (3)(7)(143)(2)(5)
Finally, 143 = ...
So, 30,030 = (3)(7)(11)(13)(2)(5)
Cheers,
Brent
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