M7MBA wrote:The Number of students learning Three subjects is as follows:
- Maths = 40
- English = 50
- Science = 35
If the Number of students learning exactly two subjects is maximum and no student learns all the three subjects, then what is the minimum number of students learning exactly one subject?
A. 0
B. 1
C. 25
D. 35
E. 45
The values in blue represent the number of students studying exactly 1 subject.
Sum of the values in blue:
125 - 2(a+b+c).
To MINIMIZE the value of this expression, we must MAXIMIZE the value of a+b+c.
Since the expression must be nonnegative, a+b+c ≤ 62.
Goal:
Choose values so that a+b+c = 62.
Since a+c belongs to the most studied subject -- English -- try to maximize a+c.
Since there are 50 English students, the greatest possible option for a+c=50, with the result that b = 62-50 = 12.
In the Venn Diagram, insert b=12 and maximize the values of b and c so that b+c = 50:

In the resulting Venn Diagram, one student studies only science, implying that the minimum number of students studying exactly one subject = 1.
The correct answer is
B.
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