Let total inters = 100

75 percent of total interns who had less than 6 hours of sleep were tired.

80 percent of total interns had fewer than 6 hours of sleep which means 5 percent of interns who had less than 6 hours of sleep.

if 80 percent of total interns had fewer than 6 hours of sleep, 20 percent of the total interns had more than 6 hours of sleep.

0.7(20) = 14 percent of interns who had more than 6 hours of sleep did not feel tired.

so 14 + 5 = 19% of total interns did not feel tired. IMO C.

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