Question

If A and B are two disjoint sets such that n(A)=20 and n(B)=30.

Then n(A-B) is equal to?​

Answer 1

Answer:

A=20

B=30

(A-B)

20-30

-10

Answer 2

$\longrightarrow \: given :$

n(A) = 20

n(B) = 30

A and B are two disjoint sets

Hence n(A n B) = 0

$\longrightarrow \: to \: find :$

n( A - B ) = ?

$\longrightarrow \: solution :$

n(A-B) = only A not B = n(A) - n(A n B)

n(A-B) = 20 - 0

n(A - B) = 20

Hence the answer is 20 = n(A-B)

______________________

more info :

✓ P(A U B) = n(A) + n(B) - n(A n B)

✓ n(A-B) = n(A) - n(A n B)

✓ n(B-A) = n(B) - n(AnB)