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allenkt: Senior | Next Rank: 100 Posts; Posts: 36; Joined: Sat Apr 14, 2007 8:06 am

by allenkt » Sun May 06, 2007 5:50 pm

Is integer n a multiple of 15?

a) n is a multiple of 20
b) n + 6 is a multiple of 3

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Source: Beat The GMAT — Data Sufficiency | Sun May 06, 2007 5:50 pm

mschling52: Master | Next Rank: 500 Posts; Posts: 105; Joined: Mon Sep 18, 2006 12:34 pm; Location: OH; Thanked: 7 times; GMAT Score:780

by mschling52 » Tue May 08, 2007 7:36 am

Is it C - Both combined sufficient?

(1) gives us that n is a multiple of 20, but 40 is not divisible by 15 while 60 is, so Not Sufficient.

(2) gives us that n+6 is a multiple of 3, hence n is also a multiple of 3. (since n+6 = 3k for some integer k, n = 3(k-2) for some integer k-2). However, 30 is divisible by 15, but 33 is not. Not Sufficient.

(1)&(2) imply that n is a multiple of 20 and of 3. Since 5 is a factor of 20, 5 and 3 will be factors of n, thus 15 is a factor of n. Sufficient.

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Stacey Koprince: GMAT Instructor; Posts: 2228; Joined: Wed Dec 27, 2006 3:28 pmFollowed by: 694 members; Location: Montreal, Canada; Thanked: 639 times; GMAT Score:780

by Stacey Koprince » Tue May 08, 2007 12:07 pm

Yep, nice job!

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