Which number does **NOT** belong to $\mathbb{Q}$ (the set of rational numbers)?
A$-5$
B$\dfrac{5}{7}$
C$\sqrt{2}$
D$3\dfrac{1}{2}$
Answer & Solution
Correct answer: C. $\sqrt{2}$
$\sqrt{2}$ is famously irrational — cannot be written as $p/q$ with $p, q$ integers.
- $-5 = -5/1$ → rational.
- $5/7$ → rational by definition.
- $3\tfrac{1}{2} = 7/2$ → rational.
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