a: \(=20.11\left(36+63+1\right)=2011\)
b: \(=17\left(85+25\right)-1200\)
\(=17\cdot110-1200=670\)
\(a=20,11.\left(36+63+1\right)=20,11.100=2011\)
\(b=17.\left(85+25\right)-1200=17.110-1200=17.\left(100+10\right)-1200\\ =17.100+17.10-1200=1700+170-1200\\ =\left(1700-1200\right)+170=500+170=670\)
\(c=\left(6\dfrac{2}{7}+\dfrac{5}{7}\right)+\left(7\dfrac{3}{5}+\dfrac{2}{5}\right)+\left(8\dfrac{2}{3}+\dfrac{1}{3}\right)\\ =\left[6+\left(\dfrac{2}{7}+\dfrac{5}{7}\right)\right]+\left[7+\left(\dfrac{3}{5}+\dfrac{2}{5}\right)\right]+\left[8+\left(\dfrac{2}{3}+\dfrac{1}{3}\right)\right]\\ =\left(6+1\right)+\left(7+1\right)+\left(8+1\right)\\ =7+8+9=24\)