n/(n+1) gmatclub

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arora007: Community Manager; Posts: 1048; Joined: Mon Aug 17, 2009 3:26 amFollowed by: 27 members; Location: India; Thanked: 51 times; GMAT Score:670

by arora007 » Mon Jul 05, 2010 8:36 am

CLOCK ur timing on this gmatclub problem

A sequence is defined as follows:

An = n/(n + 1)

If n is a positive integer, then how many of the first 100 terms of this sequence are less than 0.891?
a) 7
b) 8
c) 9
d) 10
e) 12

OA is b 8 terms are less than .891

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amising6: Master | Next Rank: 500 Posts; Posts: 294; Joined: Wed May 05, 2010 4:01 am; Location: india; Thanked: 57 times

by amising6 » Mon Jul 05, 2010 8:43 am

arora007 wrote:CLOCK ur timing on this gmatclub problem

A sequence is defined as follows:

An = n/(n + 1)

If n is a positive integer, then how many of the first 100 terms of this sequence are less than 0.891?
a) 7
b) 8
c) 9
d) 10
e) 12

OA is b 8 terms are less than .891

.89= approx .9 so
.9=9/10
so there will be 8 terms excluding 9 as 9 will give .9
1 to 8

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selango: Legendary Member; Posts: 1460; Joined: Tue Dec 29, 2009 1:28 amFollowed by: 7 members; Thanked: 135 times

by selango » Mon Jul 05, 2010 8:46 am

An=n/(n+1)

A1=1/2=0.5

.891 approx to.9 ,An<0.9

Sub n=9 ,A9=0.9

Now try n=8

A8=8/9=0.888.Remaining 7 terms also will be bw 0.5 and 0.891

So first 8 terms.

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outreach: Legendary Member; Posts: 748; Joined: Sun Jan 31, 2010 7:54 amFollowed by: 3 members; Thanked: 46 times

by outreach » Mon Jul 05, 2010 8:18 pm

i just took the middle number from the answer choice since the answers are in sorted order.
option C) 9
9/10 = 0.90. it is greater so proceed to option b

option B) 8
8/9 = 0.89

hence correct

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paridhi: Senior | Next Rank: 100 Posts; Posts: 74; Joined: Mon Jun 30, 2008 3:07 am; Thanked: 5 times

by paridhi » Mon Jul 05, 2010 9:25 pm

arora007 wrote:CLOCK ur timing on this gmatclub problem

A sequence is defined as follows:

An = n/(n + 1)

If n is a positive integer, then how many of the first 100 terms of this sequence are less than 0.891?
a) 7
b) 8
c) 9
d) 10
e) 12

OA is b 8 terms are less than .891

I have a confusion here, the question says first 100 terms of this sequence. From this how can we assume that the sequence starts with n=1?

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papgust: Community Manager; Posts: 1537; Joined: Mon Aug 10, 2009 6:10 pmFollowed by: 252 members; Thanked: 653 times

by papgust » Mon Jul 05, 2010 9:31 pm

The question says "n is a positive integer". So, you start from 1. First term of the sequence starts from 1/2 or 0.5.

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paridhi: Senior | Next Rank: 100 Posts; Posts: 74; Joined: Mon Jun 30, 2008 3:07 am; Thanked: 5 times

by paridhi » Mon Jul 05, 2010 9:48 pm

papgust wrote:The question says "n is a positive integer". So, you start from 1. First term of the sequence starts from 1/2 or 0.5.

"n is a positive integer" could also mean that the series starts with n=2 or 3 or.....

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selango: Legendary Member; Posts: 1460; Joined: Tue Dec 29, 2009 1:28 amFollowed by: 7 members; Thanked: 135 times

by selango » Mon Jul 05, 2010 10:32 pm

Yes n is a positive integer.But first 100 terms of sequence means n is from 1 to 100.

--Anand--

rsvaishu: Junior | Next Rank: 30 Posts; Posts: 13; Joined: Sat May 29, 2010 11:08 am; Thanked: 1 times

by rsvaishu » Tue Jul 06, 2010 7:02 am

if n=9
9/10 = .9 so no since less than .891

go to lesser value option b

if n = 8

8/9 = .888 yes since less than .891

so 8 terms

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