In radioactivity decay according to law $N=N_0{e}^{-\lambda t}$. Which of the following is/are true?

$\frac{N}{N_0}$ is the fraction of nuclei that will not decay

$\left(1-\frac{N}{N_0}\right)$ is the fraction of nuclei that will decay

$1-\frac{N}{N_0}=1-e^{-\lambda t}=\left(Proability that a nucleus will decay\right)$

Also $\frac{N}{N_0}={\left(\frac{1}{2}\right)}^n$ where $n=\frac{t}{T_{1/2}}$

$$\begin{gathered} \frac{N}{N_0}={\left(\frac{1}{2}\right)}^4=\frac{1}{16} \\ 1-\frac{N}{N_0}=1-\frac{1}{16}=\frac{15}{16} \end{gathered}$$

Probability that a nucleus will decay is 

$\frac{N}{N_0}={\left(\frac{1}{2}\right)}^2=\frac{1}{4}$

So fraction of nuclei that will remian after two half lives is $\frac{1}{4}or 25\%$