By prime factorisation, $\sqrt{441}$ equals

By prime factorisation, $\sqrt{441}$ equals
  1. $21$
  2. $20$
  3. $22$
  4. $19$

Solution

$441 = 3^{2} \times 7^{2}$, so $\sqrt{441} = 3 \times 7 = 21$.

Asked in: IMO

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