sequence/data suff

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BILL: Newbie | Next Rank: 10 Posts; Posts: 7; Joined: Mon Aug 18, 2008 6:21 am

by BILL » Sat Aug 23, 2008 9:52 am

In the sequence of positive numbers X1, X2, X3....what is the value of X1?

(1) xi = (xi-1)/2 for all integers i>1
(2) x5 = x4/(x4+1)

source is GMAC practice test #1, answer is C

what am I missing?

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Source: Beat The GMAT — Data Sufficiency | Sat Aug 23, 2008 9:52 am

sudhir3127: Legendary Member; Posts: 829; Joined: Mon Jul 07, 2008 10:09 pmFollowed by: 3 members; Location: INDIA; Thanked: 84 times

Re: sequence/data suff

by sudhir3127 » Sat Aug 23, 2008 10:51 am

BILL wrote:In the sequence of positive numbers X1, X2, X3....what is the value of X1?

(1) xi = (xi-1)/2 for all integers i>1
(2) x5 = x4/(x4+1)

source is GMAC practice test #1, answer is C

what am I missing?

its C

here it goes

statement 1. xi = (xi-1)/2 for all integers i>1

tells us nothing ............insufficient

statement 2. x5 = x4/(x4+1)

again nothing ..............insuffcient

combining together...

we know

xi = (xi-1)/2 thus X5 will be X4/2 ( Xi-1/2)..........................a
but statement 2 says X5 = x4/(x4+1).................................b

equate a and b

X4/2 = x4/(x4+1)

thus X4 = 1

now we can use this to find X1

thus C is the answer..

do let me know if u have any doubts...

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BILL: Newbie | Next Rank: 10 Posts; Posts: 7; Joined: Mon Aug 18, 2008 6:21 am

by BILL » Sat Aug 23, 2008 11:42 am

Great explanation, thanks for the quick responce. Much appreciated

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