Question 1201991
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In a class, 85% of the students passed a test. 40% of the students who failed the test 
received a grade lower then 30. 20% of the students who passed the test 
received a grade higher than 90. Then, what percent of students scored between 30 and 90, inclusive?
(A) 68%
(B) 71%
(C) 74%
(D) 77%
(E) 80%
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        This problem admits short,  clear and strightforward solution, as shown below.



<pre>
85% of the students passed a test; hence, 15% failed.



40% of these 15% received a grade lower then 30.

Hence, 0.4*0.15 = 0.06, or 6%, are out of our consideration.



20% of 85%, or 0.2*0.85 = 0.17 = 17%, received a grade higher than 90.

These 17% also are out of our consideration.



It is clear that these 6% set and 17% set are disjoint, since they are on opposite ends of the 100% set.

Hence and therefore, the <U>ANSWER</U> to the problem's question is  100% - 6% - 17% = 77%.   
</pre>

Solved.