Question

If $3 N \cap 7 N$ is

• A. 21 N
• B. 10 N
• C. 4 N
• D. None of these

Answer 1

Answer: (A)

21 N

Answer 2

$3 N = \{ x \in N : x$is a multiple of 3}

$7 N = \{ x \in N :$x is a multiple of 7}

∴$= \{ x \in$is a multiple of 3 and 7}

$= \{ x \in N : x$is a multiple of 3 and 7}

$= \{ x \in N :$x is a multiple of 21}=21N.