In a class of 40 pupils,30 students study biology,22 study physics and 21 study chemistry,2 study physics only,3 study study chemistry only and 7 study biology only. What is the probability that a pupil selected at random studies at least two subjects
To find the probability that a pupil selected at random studies at least two subjects, we need to find the number of students who study at least two subjects and divide it by the total number of students.
Let's first find the number of students who study at least two subjects.
Total number of students studying at least two subjects = Total number of students - Number of students who study only one subject
Number of students who study only one subject = Number of students studying biology only + Number of students studying physics only + Number of students studying chemistry only
Number of students who study only one subject = 7 + 2 + 3 = 12
Total number of students studying at least two subjects = 40 - 12 = 28
Therefore, the probability that a pupil selected at random studies at least two subjects is:
Probability = Number of students studying at least two subjects / Total number of students
Probability = 28 / 40
Probability = 7 / 10
Probability = 0.7
So, the probability that a pupil selected at random studies at least two subjects is 0.7 or 70%.