Question

The smallest set $X$ such that $X\cup$ {1, 2} = {1, 2, 3, 5, 9} is:

• A. {1, 2, 3, 5, 9}
• B. {2, 3, 5}
• C. {3, 5, 9}
• D. {3, 9}

Answer 1

The correct option is C {3, 5, 9}

$X\cup$ {1, 2} = {1, 2, 3, 5, 9}

So, set $X$ must contain the elements 3, 5 and 9, apart from any other elements.

But, since we are considering the smallest set that contains 3, 5, and 9, $X$ = {3, 5, 9}