GMAT PREP question

[aditi_bc]

Please provide solution for this GMATPREP question:

On a certain road 10% motorists exceed the posted speed limit and receive speeding ticketS, but 20% of the motorists who exceed the posted speed limit do not receive speeding tickets.What percentage of the motorists on that road exceed the posted speed limit?
A) 10 & 1/2%, B)12 & 1/2%, C)15%, D)22%, E)30%

The question appeared ambiguous to me hence couldn't solve it correctly.

[earth@work]

IMO 30%, whats the answer... i used venn diag to solve it.
overspeed ONLY=20
ticket + overspeed = 10
total overspeed = 30%

[earth@work]

IMO 30%, whats the answer... i used venn diag to solve it.
overspeed ONLY=20
ticket + overspeed = 10
total overspeed = 30%
do let me know if this is incorrect-then will try solving again

[niraj_a]

i get 30% as well. i used a double matrix and got that.

[cramya]

Refer to
https://www.beatthegmat.com/gmatprep-per ... t9304.html

Its a tricky one for sure!!

[cramya]

A different variation of that would be:

Let the total motorists be 100 on the road

10% exceed speed limit and receive tickets So lets say 10

Let x be the total number of motorists on the road who exceed the speed limit(some get tickets and some dont and we know 10 out of this x gets tickets)

20% of x exceed the speed limit but dont get tickets

Therefore 10+ .20x (20% of x) = x
.8x = 10
x = 100/8 = 12.5 %

[cramya]

Guys sorry! I think the link I posted is the best solution I have seen so far.

In my solution if I take the total motorists to be 50 then the % changes and it should not.

[earth@work]

thanks cramya, that was tricky.... i was totally wrong with calculation..thanks