from 1, to 3, to 5 to 7, notice, is simply adding 2 to get the next term.
1+2 =3, 3+2 =5 and so on.
so the common difference is 2, and the first term is of course 1.
[tex]\bf n^{th}\textit{ term of an arithmetic sequence}
\\\\
a_n=a_1+(n-1)d\qquad
\begin{cases}
n=n^{th}\ term\\
a_1=\textit{first term's value}\\
d=\textit{common difference}\\[-0.5em]
\hrulefill\\
a_1=1\\
d=2\\
n=24
\end{cases}
\\\\\\
a_{24}=1+(24-1)2\implies a_{24}=1+(23)2\implies a_{24}=1+46\implies a_{24}=47[/tex]
