Smallest natural number to multiply $72$ to make a perfect cube is

Smallest natural number to multiply $72$ to make a perfect cube is
  1. $3$
  2. $2$
  3. $6$
  4. $9$

Solution

$72 = 2^{3} \times 3^{2}$. Need one more $3$: multiply by $3$, giving $216 = 6^{3}$.

Asked in: IMO

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