Doubts..

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gmatrant: Master | Next Rank: 500 Posts; Posts: 416; Joined: Wed Oct 03, 2007 9:08 amFollowed by: 1 member; Thanked: 10 times

by gmatrant » Thu Sep 02, 2010 6:08 pm

If m =2^x*5^y*7^z and both 350 and 280 are factors of m, what is the
minimum value of xyz?
(A) 700
(B) 70
(C) 24
(D) 6
(E) 5

The probability that a certain coin will fall heads up is 50%. What is the
probability that it falls heads up on three of six tosses?
(A)41/2^6
(B)35/2^6
(C)1/2^6
(D)21/2^5
(E)5/2^4

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Source: Beat The GMAT — Problem Solving | Thu Sep 02, 2010 6:08 pm

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Rahul@gurome: GMAT Instructor; Posts: 1179; Joined: Sun Apr 11, 2010 9:07 pmFollowed by: 88 members; Location: Milpitas, CA; Thanked: 447 times

by Rahul@gurome » Thu Sep 02, 2010 6:32 pm

If m =2^x*5^y*7^z and both 350 and 280 are factors of m, what is the
minimum value of xyz?
(A) 700
(B) 70
(C) 24
(D) 6
(E) 5

Solution:

350 = 2 * 5^2 * 7 and 280 = 2^3 * 5 * 7
LCM of 350 and 280 = 2^3 * 5^2 * 7 = 1400 implies x = 3, y = 2, z = 1
So, minimum value of xyz = 3*2*1 = 6

The correct answer is [spoiler](D)[/spoiler].

Rahul Lakhani
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Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
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shibal: Master | Next Rank: 500 Posts; Posts: 345; Joined: Wed Mar 18, 2009 6:53 pm; Location: Sao Paulo-Brazil; Thanked: 12 times; GMAT Score:660

by shibal » Sat Sep 04, 2010 4:32 am

gmatrant wrote: The probability that a certain coin will fall heads up is 50%. What is the
probability that it falls heads up on three of six tosses?
(A)41/2^6
(B)35/2^6
(C)1/2^6
(D)21/2^5
(E)5/2^4

6C3/2^6 ==> 20/2^6 = 5/2^4 E

OA

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diebeatsthegmat: Legendary Member; Posts: 1119; Joined: Fri May 07, 2010 8:50 amFollowed by: 3 members; Thanked: 29 times

by diebeatsthegmat » Sun Sep 12, 2010 8:04 pm

gmatrant wrote:If m =2^x*5^y*7^z and both 350 and 280 are factors of m, what is the
minimum value of xyz?
(A) 700
(B) 70
(C) 24
(D) 6
(E) 5

The probability that a certain coin will fall heads up is 50%. What is the
probability that it falls heads up on three of six tosses?
(A)41/2^6
(B)35/2^6
(C)1/2^6
(D)21/2^5
(E)5/2^4

1. 350=7.5.2.5=2.5^2.7 and 280=4.7.2.5=2^3.5.7
thus the largest n will be 5^2.7.2^3
so 2.3.1=6
the correct answer is D
2. 500% head so 50% T thus 6 times tosses has its probability is 1/2^6
and we need 3 head time thus 3 tails : HHHTTT=6!/3!3!=20
the probability is 20/2^6=4.5/2^6=5/2^4
the answer is E

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