0.85*2.84*50=[(0.8+0.005)(2+0.8+0.04)]*50=(0.8*2+0.8*0.8+0.8*0.04+0.05*2+0.05*0.8+0.05*0.04)*50=(1.6+0.64+0.032+0.1+0.04+0.002)*50=2.414*50=2*50+0.4*50+0.01*50+0.004*50=120.7这个 我算的好像也不是很简...