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a fish colony

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a fish colony

by rahul.s » Tue Feb 23, 2010 2:49 am
A fish colony is called "unstable" if, at the end of the year, the total increase in the sum of the lengths of the fish in the colony is more than 15% greater than the sum of the lengths of the fish at the beginning of the year. In a colony of three fish, the length of the longest fish increased by 20% by the end of the year, and the length of the other two fish increased by 10% by the end of the year. Is this fish colony unstable?

(1) The original length of the longest fish was 10 inches, and the original length of the second-longest fish was 7 inches.
(2) The original length of the shortest fish was 5 inches

OA: C
Source: Knewton
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by harsh.champ » Tue Feb 23, 2010 2:56 am
rahul.s wrote:A fish colony is called "unstable" if, at the end of the year, the total increase in the sum of the lengths of the fish in the colony is more than 15% greater than the sum of the lengths of the fish at the beginning of the year. In a colony of three fish, the length of the longest fish increased by 20% by the end of the year, and the length of the other two fish increased by 10% by the end of the year. Is this fish colony unstable?

(1) The original length of the longest fish was 10 inches, and the original length of the second-longest fish was 7 inches.
(2) The original length of the shortest fish was 5 inches

OA: C
Source: Knewton
I cant understand the bold-faced part.
Is the question correctly typed??
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by rahul.s » Tue Feb 23, 2010 3:05 am
harsh.champ wrote:
rahul.s wrote:A fish colony is called "unstable" if, at the end of the year, the total increase in the sum of the lengths of the fish in the colony is more than 15% greater than the sum of the lengths of the fish at the beginning of the year. In a colony of three fish, the length of the longest fish increased by 20% by the end of the year, and the length of the other two fish increased by 10% by the end of the year. Is this fish colony unstable?

(1) The original length of the longest fish was 10 inches, and the original length of the second-longest fish was 7 inches.
(2) The original length of the shortest fish was 5 inches

OA: C
Source: Knewton
I cant understand the bold-faced part.
Is the question correctly typed??
yeah, it's correct.
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by rahul.s » Tue Feb 23, 2010 3:07 am
at the end of a year, the sum of their lengths shouldn't be greater than 15% of what it was at the start of the year. if it is greater than 15%, then they're unstable.
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by kstv » Tue Feb 23, 2010 3:24 am
To find the % growth, we need the sums of their measurement at the beginning. Percentage growth individually is given.
(1) Insuff we still need the length of the shortest.
(2) Suff.

No need to calculate, but the answer will either be negative or affirmative. So C.
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by ajith » Tue Feb 23, 2010 3:33 am
rahul.s wrote:A fish colony is called "unstable" if, at the end of the year, the total increase in the sum of the lengths of the fish in the colony is more than 15% greater than the sum of the lengths of the fish at the beginning of the year. In a colony of three fish, the length of the longest fish increased by 20% by the end of the year, and the length of the other two fish increased by 10% by the end of the year. Is this fish colony unstable?

(1) The original length of the longest fish was 10 inches, and the original length of the second-longest fish was 7 inches.
(2) The original length of the shortest fish was 5 inches

OA: C
Source: Knewton
Let x , y , z be the lengths of longest, second longest and shortest fishes respectively at the start of the year.

1. x = 10, y =7; x' = 12 , y' = 7.7 and z' = 1.1 z

The new average = (19.7+1.1z)/3
The old average = (17+z)/3

Let us take 2 cases z=7 and z=1

if z=10 ; The ratio of new and old average= (19.7+7.7)/(17+7) = 1.14
14% increase
if z= 1 ; the ratio is = (19.7+1.1)/(17+1) =1.155
15.5% increase

Not sufficient

2) Not Sufficient since it doesnt tell anything about the other two fish's ; lengths

Combining

New average = (12+7.7+5.5) /3= 25.2/3 = 8.4
Old average = (10+7+5)/3 =22/3

ratio = 25.2/22 =1.145

Less than 15% , sufficient to decide whether the colony is unstable
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