393. Several people had dinner together and had to pay 175 shillings for the bill. It turned out that two of them had no money, so each of the rest had to pay 10 shillings more than their share. How many people had dinner?
393. Let $x$ be the number of people who had lunch. It is easy to form the equation

$$
\frac{175}{x-2}-\frac{175}{x}=10
$$

from which

$$
x^{2}-2 x=35
$$

Maclaurin would solve it as follows:

$$
\begin{gathered}
x^{2}-2 x+1=36 \\
(x-1)^{2}=36 ; x-1= \pm 6 ; x_{1}=7 \text { or } x_{2}=-5
\end{gathered}
$$

The second root is not valid.