o n ( A ∪ B ∪ C ) = n ( A ) + n ( B ) + n ( C ) – n ( A ∩ B ) – n ( B ∩ C ) – n ( A ∩ C ) + n ( A ∩ B ∩ C )
Refer ExamFear Video Lessons for explanation .
Numerical : In a school there are 20 teachers who teach mathematics or physics . Of these , 12 teach mathematics and 4 teach both physics and mathematics . How many teach physics ?
Solution : Let P denote Physics teachers & M denote Maths Teacher . n ( M ) = 12 n ( M ∪ P ) = 20 n ( M ∩ P ) = 4 Applying formula n ( M ∪ P ) = n ( M ) + n ( P ) – n ( M ∩ P ) Or 20 = 12 + n ( P ) – 4 Or n ( P ) = 12 We can also solve this with Venn diagram