Question

In a class of 50 students, each one come to school by bus or by bicycle or on foot. 25 by bus, 20 by bicycle, 30 on foot and 10 students by all the three. Now how many students come to school exactly by two modes of transport?

Answer 1

Let B, C and D represent students come to school by bus, bicycle and foot respectively.

n(B ∪ C ∪ D) = 50, n(B) = 25, n(C) = 20, n(D) = 30, n(B ∩ C ∩ D) = 10

Let x, y and z represent the students come to school exactly by two modes of transport.

Let us represent the given data in Venn diagrams.

Total number of students in the class = 50

15 – x – z + x + 10 – x – y + y + 10 + z + 20 – z – y = 50

55 – x – y – z = 50

55 – 50 = x + y + z

5 = x + y + z

Number of students come to school exactly by two modes of transport = 5