=3.51×(49+51）+（50-1）×（50+1）=351+2500-1=2850
(3+0.51)*49+(30+5.1)*5.1+49*51=30*4.9+5.1*4.9+30*5.1+5.1*5.1+(50-1)*(50+1)=30*(4.9+5.1)+5.1*(4.9+5.1)+50*50-1剩下自己算下呵呵！
