Question

SIf A and B are disjoint, then $n ( A \cup B )$ is equal to.

• A. $n ( A )$
• B. $n ( B )$
• C. $n ( A ) + n ( B )$
• D.

Answer 1

Answer: (C)

$n ( A ) + n ( B )$

Answer 2

Since A and B are disjoint,

∴ $A \cap B = \phi$

$n ( A \cap B ) = 0$

Now $n ( A \cup B ) = n ( A ) + n ( B ) - n ( A \cap B )$

$= n ( A ) + n ( B ) - 0$ $= n ( A ) + n ( B )$.