Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 350,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

On a certain road 10% of the motorists exceed the posted [#permalink]
13 Dec 2007, 05:27

On a certain road 10% of the motorists exceed the posted speed limit and receive tickets, but 20% of the motorists who exceed the posted speed limit do not receive speeding tickets. What % of the motorists on the road exceed the posted speed limit?

[quote="marcodonzelli"]On a certain road 10% of the motorists exceed the posted speed limit and receive tickets, but 20% of the motorists who exceed the posted speed limit do not receive speeding tickets. What % of the motorists on the road exceed the posted speed limit?

A. 10,5%
B. 12,5%
C. 15%
D. 22%
E. 30%[/quote]

I think it's E.

The total of motorists on the road exceed the posted speed limit = those only exceed speed limit (20%) + those both exceed speed limit & receive ticket ( 10%) = 30%

I dont know if I just simply simplify the problem??

On a certain road 10% of the motorists exceed the posted speed limit and receive tickets, but 20% of the motorists who exceed the posted speed limit do not receive speeding tickets. What % of the motorists on the road exceed the posted speed limit?

A. 10,5% B. 12,5% C. 15% D. 22% E. 30%

It is B

Let's put T-total number of motorists; S - number of motorists who exceed speed limit.

So,
0.1T - number of motorists who exceed and receive tickets
0.2S - number of motorists who exceed but don't receive tickets =>0.8S - exceed and receive

On a certain road 10% of the motorists exceed the posted speed limit and receive tickets, but 20% of the motorists who exceed the posted speed limit do not receive speeding tickets. What % of the motorists on the road exceed the posted speed limit?

10 speed and get tickets
but 20% of those who speed don't receive tickets
Let X = number of people who speed
.8x = 10 (80% of speeders make up the 10 who got tickets because 20% don't get caught)
x - 12.5

Whenever I get a problem with multiple percentages (ie, subgroups), I like to draw a tree to help me see how things break out. I started with 100 motorists.

Also, really big GMAT tip which sounds deceptively simple: FOLLOW THE OF's. Whenever you are thinking about a percentage problem, always make sure you ask "percent of what?" and be sure to take the percentage of the right number. The word "OF" is a signpost for that - whatever is right after of will almost always be the right thing to use.

Whenever I get a problem with multiple percentages (ie, subgroups), I like to draw a tree to help me see how things break out. I started with 100 motorists.

Also, really big GMAT tip which sounds deceptively simple: FOLLOW THE OF's. Whenever you are thinking about a percentage problem, always make sure you ask "percent of what?" and be sure to take the percentage of the right number. The word "OF" is a signpost for that - whatever is right after of will almost always be the right thing to use.

nice one.

Thanks for the explanation. I was dam confused but the diagram (tree) cleared up doubts.

in my view,I could remove D and E directly,especially E,if e is correct,the question is very simply. the key of problem is 20% refer to those who exceed, do not receive tickets.

Wow...I'm still reeling from my HBS admit . Thank you once again to everyone who has helped me through this process. Every year, USNews releases their rankings of...

I had an interesting conversation with a friend this morning, and I realized I need to add a last word on the series of posts on my application process. Five key words:...