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The level of lead contamination in United States rivers [#permalink]
 03 Sep 2008, 20:42
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The level of lead contamination in United States rivers declined between 1975 and 1985. Federal regulations requiring a drop in industrial discharges of lead went into effect in 1975, but the major cause of the decline was a 75 percent drop in the use of leaded gasoline between 1975 and 1985.
Which of the following, if true, best supports the claim that the major cause of the decline in the level of lead contamination in United States rives was the decline in the use of leaded gasoline?
A The level of lead contamination in United States rivers fell sharply in both 1975 and 1983.
B Most of the decline in industrial discharges of lead occurred before 1976, but the largest decline in the level of river contamination occurred between 1980 and 1985.
C Levels of lead contamination in rivers fell sharply in 1975-1976 and rose very slightly over the next nine years.
D Levels of lead contamination rose in those rivers where there was reduced river flow due to drought.
E Although the use of leaded gasoline declined 75 percent between 1975 and1985, 80 percent of the decline took place in 1985.
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Re: CR lead content [#permalink]
03 Sep 2008, 20:53
ssandeepan wrote: The level of lead contamination in United States rivers declined between 1975 and 1985. Federal regulations requiring a drop in industrial discharges of lead went into effect in 1975, but the major cause of the decline was a 75 percent drop in the use of leaded gasoline between 1975 and 1985.
Which of the following, if true, best supports the claim that the major cause of the decline in the level of lead contamination in United States rives was the decline in the use of leaded gasoline?
A The level of lead contamination in United States rivers fell sharply in both 1975 and 1983.
B Most of the decline in industrial discharges of lead occurred before 1976, but the largest decline in the level of river contamination occurred between 1980 and 1985.
C Levels of lead contamination in rivers fell sharply in 1975-1976 and rose very slightly over the next nine years.
D Levels of lead contamination rose in those rivers where there was reduced river flow due to drought.
E Although the use of leaded gasoline declined 75 percent between 1975 and1985, 80 percent of the decline took place in 1985. ANS should be E. According to E, the act ran in effect in 1975. But most decline in the use of leaded gasoline took place in 1985. So, the decline of the level of lead contamination was not that much related with the act...
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Re: CR lead content [#permalink]
03 Sep 2008, 22:15
Richardson wrote: ssandeepan wrote: The level of lead contamination in United States rivers declined between 1975 and 1985. Federal regulations requiring a drop in industrial discharges of lead went into effect in 1975, but the major cause of the decline was a 75 percent drop in the use of leaded gasoline between 1975 and 1985.
Which of the following, if true, best supports the claim that the major cause of the decline in the level of lead contamination in United States rives was the decline in the use of leaded gasoline?
A The level of lead contamination in United States rivers fell sharply in both 1975 and 1983.
B Most of the decline in industrial discharges of lead occurred before 1976, but the largest decline in the level of river contamination occurred between 1980 and 1985.
C Levels of lead contamination in rivers fell sharply in 1975-1976 and rose very slightly over the next nine years.
D Levels of lead contamination rose in those rivers where there was reduced river flow due to drought.
E Although the use of leaded gasoline declined 75 percent between 1975 and1985, 80 percent of the decline took place in 1985. ANS should be E. According to E, the act ran in effect in 1975. But most decline in the use of leaded gasoline took place in 1985. So, the decline of the level of lead contamination was not that much related with the act... How can we say that decline was not much related to the act. The stem does not say that the act was repealed and E does not either. E is just showing a peak point in the decline. Our goal is to prove that 75 percent less use of leaded gasoline caused the decline in contamination and NOT industrial wastage IMO B exactly does that. B says that most of the decline happened before 76. that is in years <= 75. Largest decline happened between 80 and 85. clearly majority of the decline should have been caused by less usage of leaded gasoline. What is the OA?
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Re: CR lead content [#permalink]
04 Sep 2008, 01:05
Agree with B.
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Re: CR lead content [#permalink]
04 Sep 2008, 01:12
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Re: CR lead content [#permalink]
04 Sep 2008, 02:03
Why D cannot be right?
As per D, level of contamination rose in those rivers where there was less flow due to drought. that means, industrial discharge still increased the contamination in those rivers. However, the other rivers where flow increased due to rain, the contamination decreased as there was a drop in leaded gasoline.
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Re: CR lead content [#permalink]
04 Sep 2008, 02:18
scthakur wrote: Why D cannot be right?
As per D, level of contamination rose in those rivers where there was less flow due to drought. that means, industrial discharge still increased the contamination in those rivers. However, the other rivers where flow increased due to rain, the contamination decreased as there was a drop in leaded gasoline. D doesn't say anything. There is an unknown source of lead contamination, and these rivers dried up faster than lead contamination decreased, resulting in net increase of lead contamination of said rivers. Not relevant to the argument.
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Re: CR lead content [#permalink]
04 Sep 2008, 13:58
Agree B
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Re: CR lead content [#permalink]
04 Sep 2008, 14:18
OA is B .
If you read B properly, it states : by 1976, the discharges of lead decreased a lot but river contamination of lead did not decrease that much. So (discharges of lead ) is not directly proportional to (discharges of lead ).
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Re: CR lead content
[#permalink]
04 Sep 2008, 14:18
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