In university there are total 100 students. 15 offered mathematics only, 12 offered statistics only, 8 offered physics only, 40 offered physics and mathematics, 20 offered physics and statistics, 10 offered mathematics and statistic, 65 offered physics. Tell the number of students not offered any of three.
Explanation
Solution
Let the three sets be M (Mathematics), S (Statistics), and P (Physics).
1. Given Data:
-
Total students n(U)=100
-
Mathematics only =15
-
Statistics only =12
-
Physics only =8
-
Mathematics and Statistics n(M∩S)=10
-
Physics and Mathematics n(P∩M)=40
-
Physics and Statistics n(P∩S)=20
-
Total Physics n(P)=65
2. Finding the Intersection of all three (M∩S∩P):
Let the number of students who offered all three subjects be x.
From the data of the Physics set, we can break down the total (65) into its components:
n(P)=(Physics only)+(Physics and Math only)+(Physics and Stats only)+(All three)
Substitute these into the Physics total:
65=8+(40−x)+(20−x)+x
65=68−x
x=68−65=3
So, 3 students offered all three subjects.
3. Finding the Total number of students who offered at least one subject:
Now we calculate the other intersection parts:
-
Math and Stats only =n(M∩S)−x=10−3=7
-
Physics and Math only =40−3=37
-
Physics and Stats only =20−3=17
Total students who offered at least one subject n(M∪S∪P):
=(Math only)+(Stats only)+(Physics only)+(Math & Stats only)+(Phys & Math only)+(Phys & Stats only)+(All three)
=15+12+8+7+37+17+3
=99
4. Students not offered any of the three:
Not offered any=Total students−n(M∪S∪P)
Correct Option: (a)