The half-life of a radioactive nuclide is $40 \, \text{hours}$. Find the fraction of the substance that has decayed after $20 \, \text{hours}$.

  • A
    $\frac{\sqrt{2} + 1}{\sqrt{2}}$
  • B
    $\frac{\sqrt{2} - 1}{\sqrt{2}}$
  • C
    $\frac{\sqrt{2} - 1}{\sqrt{3}}$
  • D
    $\frac{\sqrt{3}}{\sqrt{2}}$

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