Problem 1. A student instead of multiplying a number by 506, multiplied it by the number 56, resulting in a product that was 11250 smaller. What number did the student multiply?
Solution. Let $x$ be the unknown number. Then

$$
\begin{aligned}
& x \cdot 506 - x \cdot 56 = 11250 \\
& 450 x = 11250 \\
& x = 25
\end{aligned}
$$