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help needed

by daniyatom » Sun Jul 20, 2008 9:20 am
need some help in solving the problem below. i can't solve this problem to save my life...

On a certain road, 10% of motorist who exceed the speed limit gets a ticket, and 20% of motorist who exceed the speed limit doesn't get a ticket. what is the percent of motorist on that road exceeds the speed limit?
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by pepeprepa » Sun Jul 20, 2008 1:46 pm
10% of motorist who exceed the speed limit gets a ticket
20% of motorist who exceed the speed limit doesn't get a ticket

What about the other who exceed the speed limit?
Either you have a ticket or not, I don't understand these percentages.
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by Stuart@KaplanGMAT » Sun Jul 20, 2008 2:00 pm
pepeprepa wrote:10% of motorist who exceed the speed limit gets a ticket
20% of motorist who exceed the speed limit doesn't get a ticket

What about the other who exceed the speed limit?
Either you have a ticket or not, I don't understand these percentages.
They get two tickets! :shock:

I agree, there's something wrong with the question as posted.
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by daniyatom » Sun Jul 20, 2008 4:29 pm
this was a question that i got on ETS's powerprep. the answer is 12.5%. i just don't know how to arrive to the said answer
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by Stuart@KaplanGMAT » Sun Jul 20, 2008 4:58 pm
OK, we can reverse engineer the actual question based on the answer.

Here's how the question actually reads:
On a certain road, 10% of all motorists get a ticket, and 20% of motorists who exceed the speed limit don't get a ticket. If no non-speeders get tickets, what is the percent of motorists on that road that exceed the speed limit?
So, if 20% of speeders don't get tickets, that means that 80% of speeders do get tickets.

Therefore:

10% = 80% of all speeders

1/10 = 4/5 (S)
1/10* 5/4 = S
5/40 = S
1/8 = S

and, when we convert 1/8 to a percent, we get 12.5%.
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by daniyatom » Sun Jul 20, 2008 6:31 pm
cheers
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