Question

6．脱式计算．（能简算的要简算）
3.09×3.9÷2.6         3.072÷6.4+49.7           69.6÷3.2÷2.5
3.6×2.5+7.5×3.6      0.125×3.2×0.5           60.8-36÷7.5．

Answer 1

分析 ①先算乘法再算除法．
②先算除法再算加法．
③先算3.2×2.5=8×（0.4×2.5）=8×1=8，再算69.6÷8．
④用乘法分配律计算．a×c+b×c=（a+b）×c．
⑤把3.2分成8×0.4，用8和0.125结合，0.4和0.5结合．
⑥先算除法再算减法．

解答 解：①3.09×3.9÷2.6
=12.051÷2.6
=4.635

②3.072÷6.4+49.7
=0.48+49.7
=50.18

③69.6÷3.2÷2.5
=69.6÷（3.2×2.5）
=69.6÷（8×0.4×2.5）
=69.6÷（8×1）
=69.6÷8
=8.7

④3.6×2.5+7.5×3.6
=3.6×（2.5+7.5）
=3.6×10
=36

⑤0.125×3.2×0.5
=（0.125×8）×（0.4×0.5）
=1×0.2
=0.2

⑥60.8-36÷7.5
=60.8-4.8
=56

点评 此题考查了学生对小数四则混合运算题的计算能力，以及灵活巧算的能力．