递等式计算(能简便的要用简便算法).4.89×101-4.89 0.8×(3.2-2.99÷2.3)31.7-0.5×0.7-1.65.
(1)4.89×101-4.89, =4.89×(101-1), =4.89×100, =489; (2)0.8×(3.2-2.99÷2.3), =0.8×(3.2-1.3), =0.8×1.9, =1.52; (3)31.7-0.5×0.7-1.65, =31.7-0.35-1.65, =31.7-(0.35+1.65), =31.7-2, =29.7. |
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