Please answer the following question by reasoning step-by-step.
Out of the 80 students who took the biology exam, only 2/5 of them managed to score 100%. If a score below 80% qualified as failing, and 50 percent of the remaining students who didn't score 100% managed to score over 80%, calculate the number of students who failed the exam.

24
The number of students who scored 100% is 2 / 5 * 80 = 32.

Out of the 80 students, 80 - 32 = 48 did not score 100%.

If 50% of the students who did not score 100% managed to score over 80%, then 50 / 100 * 48 = 24 students scored over 80%.

The number of students who failed is 48 - 24 = 24.

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The answer is 24