Question

If $Y$ is the smallest set such that
$Y\cup \{1,2\}=\{1,2,3,5,9\}$, then $Y$ is equal to

• A. $\{1,2,3,5,9\}$
• B. $\{3,5,9\}$
• C. $\{1,2\}$
• D. None of these

Answer 1

Answer: (B)

Since $Y\cup \{1,2\}=\{1,2,3,5,9\}$, then the set $Y$ must contain $3$, $5$, $9$. Since the set $Y$ is smallest, we have $Y=\{3,5,9\}$.