Question 1201991
85% passed the test.
15% failed.
40% of the students who failed received a grade lower than 30.
that means 60% of the student who failed received a grade greater then or equal to 30.
20% of the students who passed the test received a grade higher than 90.
that means 80% of the students who passed received a grade lower than or equal to 90.


since 85% passed the test, then 80% * 85% received a grade less than or equal to 90.
since 15% failed the test, then 60% * 15% received a grade greater than or equal to 30.
you have:
.8 * .85 = 68% passed the test and received a grade less than or equal to 90.
.6 * .15 = 9% failed the test and received a grade greater than or equal to 30.
total percent that received a grade between 30 and 90 would be 68% + 9% = 77%.


to see if this makes sense, assume that 1000 students took the test.
85% passed, so 850 passed and 150 failed.
40% of the student who failed the test gor a grade lower than 30.
that would be .4 * 150 = 60 who got a greae lower than 30.
that leaves 90 who failed and got a grade greater than or equal to 30.
20% of the students who passed the test got a grade higher than 90.
.2 * 850 = 170 who got a grade higher than 90.
that leaves 680 who passed and got a grade less than or equal to 90.
total between 30 and 90 would be 680 + 90 = 770
770/1000 = .77 = 77%.
this confirms the solution is correct.
looks like selection D is your answer.