一、下面的计算对吗?对的画“√”,错的画“×”,并改正。(每小题6分,共12分) 1. 4.9-1.23+2.77 改正: =4.9-(1.23+2.77) =4.9-4 =0.9 ( ) 2. 18.78-(8.78-4.56) 改正: =18.78-8.78-4.56 =10-4.56 =5.44 ( ) 二、计算下面各题,能简算的要简算。(每小题4分,共40分) 8.26-1.54-5.46 7.34+6.29+3.66 19.87+24.79-9.87 4.03-2.38-1.62+5.97 16.65-2.88+3.35-1.12 0.9+0.99+0.999