Question

if n(A-B)=18,n(A union B)=70,n(A intersection B)=25 find n(B)?
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Answer 1

n(AuB) = n(A) + n (B) -n(AnB) —————-1

We have n(AnB) = 25 and n(A-B) = 18

With these 2 we can calculate n(A)

n(A-B) = n(A) - n(AnB)

18 = n(A) - 25

=> n(A) = 18 + 25 = 43

now to calculate n(B) we can substitute all the values in equation 1

70 = 43+ n(B) - 25

70 = n(B) + 18

n(B) = 70–18 = 52

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