We can use the principle of inclusion and exclusion to solve this problem.
If 24 students read physics, and 9 of them also read mathematics, then the number of students who only read physics is 24 - 9 = 15.
Similarly, if 21 students read mathematics, and 9 of them also read physics, then the number of students who only read mathematics is 21 - 9 = 12.
Now we can use the formula:
Total number of students = Number who read only physics + Number who read only mathematics + Number who read both
Total number of students = 15 + 12 + 9 = 36
Therefore, there are 36 students in the class.
In a class, 24 students read physics 21 read mathematics and 9 read both physics and mathematics. If each student read at least one of the two subjects, find the number of students in the class.
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