Question

我會(huì)口算．
0.8×4=
2.5×100=
0.06×7=
0.5×100=
1.3×5=
4.2×3=

Answer 1

分析：①先算8×4=32，然后從后數(shù)出兩位，點(diǎn)上小數(shù)點(diǎn)即可；②把2.5擴(kuò)大100倍，就是把2.5的小數(shù)點(diǎn)向右移動(dòng)兩位；③先算6×7=42，然后從后數(shù)出兩位，點(diǎn)上小數(shù)點(diǎn)即可；④把0.5擴(kuò)大100倍，就是把0.5的小數(shù)點(diǎn)向右移動(dòng)兩位；⑤先算13×5=65，然后從后數(shù)出一位，點(diǎn)上小數(shù)點(diǎn)即可；⑥先算42×3=126，然后從后數(shù)出一位，點(diǎn)上小數(shù)點(diǎn)即可．

解答：解：0.8×4=3.2
2.5×100=250
0.06×7=0.42
0.5×100=50
1.3×5=6.5
4.2×3=12.6．

點(diǎn)評(píng)：此題考查了小數(shù)的乘法計(jì)算，先算整數(shù)乘整數(shù)，再根據(jù)小數(shù)點(diǎn)的位數(shù)，點(diǎn)上小數(shù)點(diǎn)即可．