Num Prop

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vinviper1: Master | Next Rank: 500 Posts; Posts: 222; Joined: Tue Mar 25, 2008 3:52 pm; Thanked: 2 times

by vinviper1 » Thu Apr 17, 2008 6:30 am

Thanks!

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Source: Beat The GMAT — Data Sufficiency | Thu Apr 17, 2008 6:30 am

simplyjat: Master | Next Rank: 500 Posts; Posts: 423; Joined: Thu Dec 27, 2007 1:29 amFollowed by: 2 members; Location: Hyderabad, India; Thanked: 36 times; GMAT Score:770

by simplyjat » Thu Apr 17, 2008 8:47 am

Answer is D.
If the number contains 5 and 2 as one of the prime factors, the number will be a multiple of 10.
A tells us that number contains 7, 5, and 2 as prime factors and we can say that units place will be zero
B tells us that there are five 5s and seven 2s and we can conclude that not only units digit, but also tens, hundreds, thousands, ten thousands digit will also be zero

simplyjat

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vinviper1: Master | Next Rank: 500 Posts; Posts: 222; Joined: Tue Mar 25, 2008 3:52 pm; Thanked: 2 times

by vinviper1 » Fri Apr 18, 2008 11:12 am

What makes you start out with prime numbers? Thanks.

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

by Stuart@KaplanGMAT » Fri Apr 18, 2008 12:15 pm

A note about dealing with statement (2).

We can use statement (2) to calculate the value of N. Lord knows we don't want to do so, but we could if we were really bored.

Since we can calculate the value of N, we can answer ANY question about N. So, without even thinking too much about (2), we know that it's going to be sufficient.

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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Musiq: Senior | Next Rank: 100 Posts; Posts: 93; Joined: Thu Apr 10, 2008 1:42 pm; Location: Chicago; Thanked: 20 times

by Musiq » Fri Apr 18, 2008 6:03 pm

vinviper1 wrote:What makes you start out with prime numbers? Thanks.

Solid question.

Prime numbers are the most IRREDUCIBLE forms of any given number.

So, for example 100 can be written as (2) (2) (5) (5)

There is no simpler form than this. So from here we can look at the properties of 100 very easily.

Another glaring clue in this question is that Statement 2 is already Prime factorised.
That should also tell us that Prime Factorisation is the way to go.

For love, not money.

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