Вычислите: a) 3,9-(6,7-23,3)+(-2,3+1,8) б) (-3 5/6 + 10 3/8) - 2 3/4 (/ - означает дробь)

3.9 - (6.7 - 23.3) + (-2.3 + 1.8) = 3.9 - 6.7 + 23.3 - 2.3 + 1.8 = 27.2 + 1.8 - 9 = 29 - 9 = 20

$(-3 \frac{5}{6} +10 \frac{3}{8} )-2 \frac{3}{4} =( \frac{83}{8} - \frac{35}{6} )- \frac{11}{4}=( \frac{83*3}{24} - \frac{35*4}{24} )- \frac{11}{4}= \\ \\= \frac{249-140}{24}- \frac{11}{4}=\frac{109}{24}- \frac{11*6}{24}=\frac{109-66}{24}= \frac{43}{24}$