Пусть x - искомое число. Тогда:
\(x - 1 \frac{2}{5} = 8 \frac{17}{20} - 4 \frac{7}{10}\)
\(x - 1 \frac{2}{5} = 8 \frac{17}{20} - 4 \frac{14}{20}\)
\(x - 1 \frac{2}{5} = 4 \frac{3}{20}\)
\(x = 4 \frac{3}{20} + 1 \frac{2}{5}\)
\(x = 4 \frac{3}{20} + 1 \frac{8}{20}\)
\(x = 5 \frac{11}{20}\)