1000 DS Sec-4, Q-11

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akg_gmat: Junior | Next Rank: 30 Posts; Posts: 16; Joined: Tue Jul 29, 2008 12:13 pm; Thanked: 1 times

1000 DS Sec-4, Q-11

by akg_gmat » Wed Aug 06, 2008 8:15 pm

Plz explain...

According to me, the answer is A

What is the value of x?
(1) When x is multiplied by 8, the result is between 50 and 60.
(2) When x is doubled, the result is between 10 and 15.

OA: E

Thanx in advance...[/spoiler]

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Source: Beat The GMAT — Data Sufficiency | Wed Aug 06, 2008 8:15 pm

P_mashru: Senior | Next Rank: 100 Posts; Posts: 43; Joined: Wed Jun 11, 2008 5:03 am; Location: Mumbai; GMAT Score:530

by P_mashru » Wed Aug 06, 2008 9:55 pm

question ask about value of X, without any specification (non zero, +ve, -ve, fraction)

1) is suff only if x is given as positive integer but same condition is not given. not suff

2) is not suff even if x is given as positive integer b'se of ambiguity, weather x=6 or 7. not suff

combining 1) & 2) is not suff b'se 1) says 6 & 7 while 1) wants 8

Answer E

I am I

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Ian Stewart: GMAT Instructor; Posts: 2623; Joined: Mon Jun 02, 2008 3:17 am; Location: Montreal; Thanked: 1090 times; Followed by:355 members; GMAT Score:780

Re: 1000 DS Sec-4, Q-11

by Ian Stewart » Thu Aug 07, 2008 4:16 am

akg_gmat wrote:Plz explain...
According to me, the answer is A

What is the value of x?
(1) When x is multiplied by 8, the result is between 50 and 60.
(2) When x is doubled, the result is between 10 and 15.

OA: E

Thanx in advance...[/spoiler]

If you answered A, I'm sure you fell into one of the more common traps in Data Sufficiency- you assumed x was a positive integer. Unless you're told that, you cannot assume that. From 1), all we know is that:

50 < 8x < 60
50/8 < x < 60/8
6.25 < x < 7.5

So x might be 6.88, or x might be 7. Insufficient.

From 2), all we know is that
10 < 2x < 15
5 < x < 7.5

Together, we still only know that 6.25 < x < 7.5. So the answer is E.

For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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