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# During a one-year study, biologists observed the number of ﬁsh in a ce

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Math Expert
Joined: 02 Sep 2009
Posts: 51100
During a one-year study, biologists observed the number of ﬁsh in a ce  [#permalink]

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15 Jul 2018, 07:54
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Difficulty:

15% (low)

Question Stats:

79% (01:32) correct 21% (01:41) wrong based on 48 sessions

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During a one-year study, biologists observed the number of ﬁsh in a certain pond as well as the percent of the ﬁsh that were catﬁsh. At the beginning of the year, there were 300 ﬁsh in the pond, of which 15 percent were catﬁsh; and at the end of the year, there were 400 ﬁsh in the pond, of which 10 percent were catﬁsh. From the beginning of the year to the end of the year, the number of catﬁsh in the pond

A. decreased by more than 5%
B. decreased by 5%
C. did not change
D. increased by 5%
E. increased by more than 5%

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Joined: 13 Feb 2018
Posts: 135
Re: During a one-year study, biologists observed the number of ﬁsh in a ce  [#permalink]

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15 Jul 2018, 12:13
2003 --> 300 fish, 15% catfish. 300*0.15=45
2004 --> 400 fish, 10% catfish, 400*0.1=40

Decrease is obvious, lets calculate the % change
45-40=5 $$\frac{5}{45}$$*100~11%

IMO
Ans: A
Math Expert
Joined: 02 Aug 2009
Posts: 7099
Re: During a one-year study, biologists observed the number of ﬁsh in a ce  [#permalink]

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15 Jul 2018, 17:16
1
Bunuel wrote:
During a one-year study, biologists observed the number of ﬁsh in a certain pond as well as the percent of the ﬁsh that were catﬁsh. At the beginning of the year, there were 300 ﬁsh in the pond, of which 15 percent were catﬁsh; and at the end of the year, there were 400 ﬁsh in the pond, of which 10 percent were catﬁsh. From the beginning of the year to the end of the year, the number of catﬁsh in the pond

A. decreased by more than 5%
B. decreased by 5%
C. did not change
D. increased by 5%
E. increased by more than 5%

Change in catfish 15% of 300 -10% of 400=$$300*\frac{15}{100}-400*\frac{10}{100}=45-40=5$$

Now all answer choices are related to 5% which actually means 5 in 100.
But here the decrease of 5 has been over 45, which is greater than 5 in 100.
Thus decreased by more than 5%

A
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1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

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Re: During a one-year study, biologists observed the number of ﬁsh in a ce &nbs [#permalink] 15 Jul 2018, 17:16
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