Question

Let $A=\{$ multiples of $3$ less than $20\}$ and $B=\{$ multiples of $5$ less than $20\}$. Then $A\cap B$ is

• A. $\{3,5\}$
• B. $\{5,9\}$
• C. $\left\{15\right\}$
• D. $\varphi$

Answer 1

Answer: (C)

$\left\{15\right\}$

$A=\{$ multiples of $3$ less than $20\}$

$=\{3,6,9,12,15,18\}$

$B=\{$ multiples of $5$ less than $20\}$

$=\{5,10,15\}$

Therefore, $A\cap B=\left\{15\right\}$.