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lead contamination

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by crackinggmat » Sat Aug 14, 2010 3:58 pm
15. 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 and 1985, 80 percent of the decline took place in 1985.








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by beatthegmatinsept » Sat Aug 14, 2010 5:29 pm
crackinggmat wrote:15. 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 and 1985, 80 percent of the decline took place in 1985.

b
Touch one. Took me a little over 2 minutes to get to the one choice that I did not eliminate and it happened to be the answer.
A - Irrelevant
C - Irrelevant or weakens our conclusion.
D - Irreleant
E - Irrelevant
[spoiler]
B - because it tells you that even though industrial discharges of lead were reduced starting 1975, the most decline occurred before 1976. While the decline in the river occurred between 1980 and 1985. This shows that Federal regulations requiring a drop in industrial discharges of lead was NOT a major cause of the decline in the level of lead contamination in United States rivers. [/spoiler]
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by paddle_sweep » Sat Aug 14, 2010 9:22 pm
It looks to me that none of the answers support the claim. How 'B' supports the claim?
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by paes » Wed Aug 18, 2010 6:23 pm
IMO B

very tough, very good question.

I took 3 min to solve

B kills the alternate possibility -> [Federal regulation responsible for reduction]
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by FightWithGMAT » Thu Aug 19, 2010 6:57 am
crackinggmat wrote:15. 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 and 1985, 80 percent of the decline took place in 1985.

I like the question.

I was confused b/w B and E

Actually both are good contenders. I don't know why somebody mentioned E as irrelevant.

So

Analyze this----

X= Decline in lead discharge
Y= Decline in lead gasoline usage
Z= Decline in lead in RIVERS

Premise says that

X causes Z

Conclusion says that

Y causes Z

We need to support the conclusion

B says that when X happens then Z does not happen.

Precisely, X and Z do not happen in same time frame so the casual relationship is not possible.
X happens before 1976 whereas Z happens after 1980.

So this eliminates the likelihood that X caused Z.

THIS IS A STRONG CASE

NOW there is a weaker version of strengthener also....E

E validates the data that YES there was 75% decline in lead gasoline usage but creates very minimal impact on the conclusion. We will have a hard time to prove that X did not cause Z, though Y is there.

B kicks E out







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