On a certain road, 10 percent of the motorists exceed the posted speed limit and receive speeding tickets, but 20 percent of the motorists who exceed the posted speed limit do not receive speeding tickets. What percent of the motorists on that road exceed the posted speed limit ?
(A)10.5%
(B)12.5%
(C) 15%
(D) 22%
(E) 30%
Plug in motorists = 100.
.1*100 = 10 motorists who exceed the speed limit and receive speeding tickets.
Since 20% of the motorists who exceed the speed limit don't get tickets, 80% do.
10 is 80% of what number?
Answer choice C:
.8*15 = 12. Too big. Eliminate C, D and E.
Answer choice B:
.8*12.5 = 10. Success!
The correct answer is B.
(Of course, we also could solve algebraically: .8x = 10, x=10/.8 = 100/8 = 12.5.)
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