Thanks for the post whiplash2411. However, there is an easier and faster way to do this.
Math = 53
Chemistry = 88
English = 58
Total = 199This total counts x, y, z twice (students taking 2 classes) and 6 thrice (students taking 3 classes). We need to count these only once to arrive at the number of students taking exactly 2 classes.
First get rid of the double counting by subtracting the actual number of students from the total above. Deal with the triple counting in the next step.
Total = 199
No. of students =(150)
Remaining = 49Since 6 has been counted thrice, subtract 6 twice (6*2 = 12) from the remainder to count it exactly once.
Remaining = 49
Subtract 12 =(12)
Final = 37Thus, the number of students taking exactly 2 classes is 37.
Hope this helps