Solve both parts and justify the conditions used. Part A: Does “interesting books” specify a well-defined set? Repair the description. Part B: Count the distinct elements.

01 / Standard#Your turn

\begin{gathered}\text{B: }A=\{7,8,7,9\}\end{gathered}

Skills and prerequisite lessons

Working and explanation

BUILD THE REASONING

Hint 1

A: Check the membership rule and count distinct objects.

Hint 2

B: Check the membership rule and count distinct objects.

Worked solution

Part A reasoning
Check the membership rule and count distinct objects.
Different readers may disagree about membership. Fix a catalogue and a publication year to make membership decidable.
Set membership must be definite rather than a personal preference.
Part B reasoning
Check the membership rule and count distinct objects.
Calculate or simplify this relation.
$A=\{7,8,9\};\quad |A|=3$
Order and repetition do not change a set.

A: No; use an objective criterion such as books published in a fixed year. B: The requested value is 3.

Checks and common pitfalls: Set membership must be definite rather than a personal preference. Order and repetition do not change a set.

Reasoning checklist · self / teacher assessment

Think first. Reveal a hint when the class is ready.

Sets and commonly used logic: mixed assessment