4. Вычислите: а) 1-3,21 + 1-1,91 – 12,251; б) $$1\frac{17}{48}: 1-2\frac{5}{6}$$.

a) $$1 - 3,21 + 1 - 1,91 - 12,251 = -3,21 - 1,91 - 12,251 + 2 = -15,371$$ б) $$1\frac{17}{48}: 1-2\frac{5}{6}$$ =$$\frac{65}{48}:\frac{11}{6}$$ =$$\frac{65}{48}*\frac{6}{11}$$ =$$\frac{65}{8}*\frac{1}{11}$$ = $$\frac{65}{88}$$