Total number of terms in $(x+a)^{n}-(x-a)^{n}$
$=\begin{cases}\frac{n+1}{2} & \text { if } n \text { is odd } \\ \frac{n}{2} & \text { if } n \text { is even }\end{cases}$
$\therefore $ Total number of terms in the expansion of
$(x+a)^{47}-(x-a)^{47}=\frac{47+1}{2} [\because n$ is odd $]$
$=\frac{48}{2} $
$=24 $