Page 34 - Math SL HB Sem 3

> Union (OR)
AUB

This represents either event,4 occurs or event B occurs (or both occur).
On a Venn diagram, it is the region in set A and set B, as shaded below:

;A B
I

,
t :
U

The Venn diagram also helps us understand that:

n(AuB) -n(A) +n(B) - n(A^B)

lf we divide the above equation by n(U), we obtain

P(AuB) -P(A) +P(B) - P(AnB)

This formula holds for all cases

'\. Example:

Consider n(U) = LZ,n(A) = 5, n(B) = 3and n(A nB) = 1, find P(/ uB).

\ Sol u tion

We may now choose between two methods:
i) Drawing Venn diagram

ii) Using the Probability formula

The results obtained from both methods agree

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