50. In the numerator of the fraction, there is a number whose leftmost digit is 1, followed by 1989 sixes. In the denominator, there is a number whose rightmost digit is 4, and before it, to the left, there are 1989 sixes. Vasya simplified this fraction by crossing out all the sixes in the numerator and the denominator, and obtained $\frac{1}{4}$. Is the result obtained by Vasya correct? Can the correctness of the solution be judged only by the answer?
50. If the numerator $166 \ldots 6$ is multiplied by 4, we get $66 \ldots 64$. Therefore, $\frac{166 \ldots 6}{66 \ldots 64}=\frac{1}{4}$. The answer is indeed correct with this set of digits, but this does not mean that such cancellation is valid. For example, if you replace the sixes with fives or any other digits, the answer will be incorrect.