Nuclear Chemistry

The number of molecules undecayed at any time t, is given by
$N = \dfrac{N_{0}}{2^{n}}$
Where $n = \dfrac{t}{t_{0.5}}$
Substituting we get,
$n = 4$
$N = \dfrac{N_{0}}{16}$
$\dfrac{N}{N_{0}} \times 100 = \dfrac{100}{16} = 6.25$