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petocities
GMAT 2: 690 Q49 V35
Posts: 17
24 Oct 2015, 12:52
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B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
5%
(low)
Question Stats:
86% (01:40) correct
14%
(01:58)
wrong
based on 445
sessions
History
Date
Time
Result
Not Attempted Yet
The formula for the surface of a sphere is \(S=4πr^2\). Two lead balls have radii 3 inches and 6 inches, respectively. A third ball has surface area equal to the sum of the surface areas of the two smaller balls. What is the radius, in inches, of the third ball?
It's not really a hard question, but I got it wrong because I didn't take enough time to read carefully the question. So i'll just leave it here for others to avoid my mistake.
Good luck ya'll
PS: Difficulty is probably under 600, but couldn't edit the tags
- (A) \(3\sqrt{10}\)
(B) \(3\sqrt{5}\)
(C) \(36π\)
(D) \(45π\)
(E) \(180π\)
It's not really a hard question, but I got it wrong because I didn't take enough time to read carefully the question. So i'll just leave it here for others to avoid my mistake.
Good luck ya'll
PS: Difficulty is probably under 600, but couldn't edit the tags
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24 Oct 2015, 13:28
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petocities
The correct answer is B.
The surface area of the bigger sphere is = 4π (3^2 +6^2) = 4πr^2
4π (9 + 36) = 4πr^2
45 = r^2
r = \sqrt{45}
= 3 \sqrt{5}
The correct answer is B.
The surface area of the bigger sphere is = 4π (3^2 +6^2) = 4πr^2
4π (9 + 36) = 4πr^2
45 = r^2
r = \sqrt{45}
= 3 \sqrt{5}
General Discussion
petocities
25 Oct 2015, 10:45
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erratic15
Yeah, upon revising my calculations I got it right, but on my first time I stopped at 4π(9+36) = 180π. Since that's (E), I just selected it. That's the silly mistake that one has to avoid!
