Answer:
210
Explanation:
Given:
Medals in sports = 40
Medals in dance = 25
Medals in music = 212
Total students that received medals = 55
Total students that received medals in all three categories = 6
Required:
How many students get medals in exactly two of these categories?
Take the following:
A = set of persons who got medals in sports.
B = set of persons who got medals in dance
C = set of persons who got medals in music.
Therefore,
n(A) = 40
n(B) = 25
n(C) = 212
n(A∪B∪C)= 55
n(A∩B∩C)= 6
To find how many students get medals in exactly two of these categories, we have:
n(A∩B) + n(B∩C) + n(A∩C) −3*n(A∩B∩C)
=n(A∩B) + n(B∩C) + n(A∩C) −3*6 ……............... (1)
n(A∪B∪C)=n(A)+n(B)+n(C)−n(A∩B)−n(B∩C)−n(A∩C)+n(A∩B∩C)
Thus, n(A∩B)+n(B∩C)+n(A∩C)=n(A)+n(B)+n(C)+n(A∩B∩C)−n(A∪B∪C)
Using equation 1:
=n(A)+n(B)+n(C)+n(A∩B∩C)−n(A∪B∪C)−18
Substitute values in the equation:
= 40 + 25 + 212 + 6 − 55 − 18
= 283 - 73
= 210
Number of students that get medals in exactly two of these categories are 210