7142.85÷3.7÷2.7×1.7×0.7.
=7142.85÷37÷27×17×7
=7142.85×7÷999×17
=49999.95÷999×17
=50.05×17
=850.85
99×1.01×77.78+66.66×33.33
=99×（1+0.01）×77.78+33.33×（2+1）
=99.99×77.78+99.99
=99.99×78.78
=（100-0.01）×78.78
=7878-0.7878
=7877.2122