a) Ta có: \(8\cdot39\cdot125\)
\(=\left(8\cdot125\right)\cdot39\)
\(=1000\cdot39=39000\)
b) Ta có: \(49\cdot77-30^2+23\cdot49\)
\(=49\cdot77+49\cdot23-30^2\)
\(=49\cdot\left(77+23\right)-900\)
\(=49\cdot100-9\cdot100\)
\(=100\cdot\left(49-9\right)\)
\(=100\cdot40=4000\)
c) Ta có: \(\frac{2340}{5\cdot89-\left(125+5\cdot7^2\right)+5\cdot11}\)
\(=\frac{2340}{5\left(89+11\right)-125-5\cdot7^2}\)
\(=\frac{2340}{5\cdot100-5\cdot25-5\cdot49}\)
\(=\frac{2340}{5\left(100-25-49\right)}=\frac{2340}{5\cdot26}=\frac{2340}{130}=18\)
