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Faces - DS

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karthikpandian19: Legendary Member; Posts: 1665; Joined: Thu Nov 03, 2011 7:04 pmFollowed by: 70 members; Thanked: 165 times

by karthikpandian19 » Wed Dec 14, 2011 12:43 am

What fractional part of the total surface area of cube C is red?
(1) Each of 3 faces of C is exactly 1/2 red.
(2) Each of 3 faces of C is entirely white.

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Source: Beat The GMAT — Data Sufficiency | Wed Dec 14, 2011 12:43 am

rijul007: Legendary Member; Posts: 588; Joined: Sun Oct 16, 2011 9:42 amFollowed by: 9 members; Location: New Delhi, India; Thanked: 130 times; GMAT Score:720

by rijul007 » Wed Dec 14, 2011 1:21 am

What fractional part of the total surface area of cube C is red?
(1) Each of 3 faces of C is exactly 1/2 red.
(2) Each of 3 faces of C is entirely white.

(1) Each of 3 faces of C is exactly 1/2 red.

We dont know what fraction of other 3 faces are red

Insufficient

(2) Each of 3 faces of C is entirely white.

Again we dont know what fraction of other faces is red

Combing the two statements
Each of 3 faces of C is exactly 1/2 red.
Each of 3 faces of C is entirely white.

We know that out of 6 faces, area of exactly 3 facs is exactly 1/2 red
Fraction part = (3/2)/6 = 1/4

Option C

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Wed Dec 14, 2011 2:22 am

karthikpandian19 wrote:What fractional part of the total surface area of cube C is red?
(1) Each of 3 faces of C is exactly 1/2 red.
(2) Each of 3 faces of C is entirely white.

(1) Each of 3 faces of C is exactly 1/2 red but nothing has been said about the other 3 faces, some fraction of the other 3 faces may be red, about which we are not sure; NOT sufficient.

(2) Each of 3 faces of C is entirely white but again nothing has been said about the other 3 faces; NOT sufficient.

Combining (1) and (2), we clearly know that 1/2 of 3 faces is red while the other 3 faces are entirely white, so fractional part of the total surface area of cube C, which is red = 1.5/6 = 1/4; SUFFICIENT.

The correct answer is C.

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ArunangsuSahu: Master | Next Rank: 500 Posts; Posts: 382; Joined: Thu Mar 31, 2011 5:47 pm; Thanked: 15 times

by ArunangsuSahu » Fri Dec 30, 2011 8:31 am

No need to SOLVE

1) No info about the remaining 3 faces. They can be full red or white. INSUFFICIENT
2) No info about the remaining three faces. They can be half Red or Full Red. INSUFFICIENT

COMBINING, It gives 6 areas.. SO SUFFICIENT

(C) is t he answer

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