48. On the sheet, several non-zero numbers are written, each of which is equal to half the sum of the others. How many numbers are written?
48. Let there be $n$ numbers, then

$$
\begin{aligned}
a_{1} & =\frac{a_{2}+a_{3}+\ldots a_{n}}{2} ; \\
a_{2} & =\frac{a_{1}+a_{3}+\ldots+a_{n}}{2} ; \\
\ldots & \ldots \ldots \ldots+a_{n-1} \\
a_{n} & =\frac{a_{1}+a_{2}+\ldots+a_{n}}{2} ; \\
2\left(a_{1}\right. & \left.+a_{2}+\ldots+a_{n}\right)=(n-1) \cdot\left(a_{1}+a_{2}+\ldots+a_{n}\right), \text { hence } 2=n-1 ; n=3 .
\end{aligned}
$$

Thus, there were 3 numbers written.