QuestionJuly 15, 2025

In a survey of 200 students, 70 were taking mathematics and 50 were taking psychology. a) What is the least number of students who could have been taking both courses? b) What is the greatest number of students who could have been taking both courses? c) What is the greatest number of students who could have been taking neither course? a) The least number of students who could have been taking both courses is square

In a survey of 200 students, 70 were taking mathematics and 50 were taking psychology. a) What is the least number of students who could have been taking both courses? b) What is the greatest number of students who could have been taking both courses? c) What is the greatest number of students who could have been taking neither course? a) The least number of students who could have been taking both courses is square
In a survey of 200 students, 70 were taking mathematics and 50 were taking psychology.
a) What is the least number of students who could have been taking both courses?
b) What is the greatest number of students who could have been taking both courses?
c) What is the greatest number of students who could have been taking neither course?
a) The least number of students who could have been taking both courses is square

Solution
3.9(279 votes)

Answer

a) 20 Explanation 1. Calculate the least number of students taking both courses Use the formula for union: n(A \cup B) = n(A) + n(B) - n(A \cap B). For the least overlap, assume all others are distinct. Thus, n(A \cup B) \leq 200. So, 70 + 50 - n(A \cap B) \leq 200. Solving gives n(A \cap B) \geq 120. 2. Calculate the greatest number of students taking both courses For maximum overlap, assume all students in one course are also in the other. The smaller group size is the limit: \min(70, 50) = 50. 3. Calculate the greatest number of students taking neither course Subtract the union from total students: 200 - (70 + 50 - n(A \cap B)). For minimum overlap, use n(A \cap B) = 0: 200 - 120 = 80.

Explanation

1. Calculate the least number of students taking both courses<br /> Use the formula for union: $n(A \cup B) = n(A) + n(B) - n(A \cap B)$. For the least overlap, assume all others are distinct. Thus, $n(A \cup B) \leq 200$. So, $70 + 50 - n(A \cap B) \leq 200$. Solving gives $n(A \cap B) \geq 120$.<br /><br />2. Calculate the greatest number of students taking both courses<br /> For maximum overlap, assume all students in one course are also in the other. The smaller group size is the limit: $\min(70, 50) = 50$.<br /><br />3. Calculate the greatest number of students taking neither course<br /> Subtract the union from total students: $200 - (70 + 50 - n(A \cap B))$. For minimum overlap, use $n(A \cap B) = 0$: $200 - 120 = 80$.
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