题目内容
用简便方法计算
①4.85×3
-3.6+6.15×3
②0.025×999×2.8×40÷2
③(
-
)×23+25÷71+15
÷23
④9.81×0.1+0.5×98.1+0.049×981
⑤1000+999-998-997+996+995-994-993+…+104+103-102-101.
①4.85×3
3 |
5 |
3 |
5 |
②0.025×999×2.8×40÷2
4 |
5 |
③(
2 |
71 |
1 |
69 |
1 |
3 |
④9.81×0.1+0.5×98.1+0.049×981
⑤1000+999-998-997+996+995-994-993+…+104+103-102-101.
分析:①把3
化成3.6,由乘法分配律进行简算即可;
②把2
化成2.8,根据乘法交换和结合律进行简算即可;
③现根据乘法分配律把(
-
)×23展开,然后再根据乘法分配律进行简算即可;
④根据积不变的规律,把每一项都化成9.81乘几,再根据乘法分配律进行简算即可;
⑤可先观察题型,经过分析可以知道:由左到右每4个数的运算结果都为4,也就可以看为每个数的运算结果为1,从101到1000一共900个数,进行计算即可;
3 |
5 |
②把2
4 |
5 |
③现根据乘法分配律把(
2 |
71 |
1 |
69 |
④根据积不变的规律,把每一项都化成9.81乘几,再根据乘法分配律进行简算即可;
⑤可先观察题型,经过分析可以知道:由左到右每4个数的运算结果都为4,也就可以看为每个数的运算结果为1,从101到1000一共900个数,进行计算即可;
解答:解:①4.85×3
-3.6+6.15×3
,
=4.85×3.6-3.6+6.15×3.6,
=(4.85-1+6.15)×3.6,
=10×3.6,
=36;
②0.025×999×2.8×40÷2
,
=0.025×999×2.8×40÷2.8,
=(0.025×40)×999×(2.8÷2.8),
=1×999×1,
=999;
③(
-
)×23+25÷71+15
÷23,
=
-
+
+
×
,
=(
+
)-
+
,
=1-
+
,
=
-
+
,
=
;
④9.81×0.1+0.5×98.1+0.049×981,
=9.81×0.1+5×9.81+4.9×9.81,
=9.81×(0.1+5+4.9),
=9.81×10
=98.1;
⑤1000+999-998-997+996+995-994-993+…+104+103-102-101
=(1000+999-998-997)+(996+995-994-993)+…+(104+103-102-101)
=4+4+…+4
=4×(900÷4)
=4×900÷4
=900.
3 |
5 |
3 |
5 |
=4.85×3.6-3.6+6.15×3.6,
=(4.85-1+6.15)×3.6,
=10×3.6,
=36;
②0.025×999×2.8×40÷2
4 |
5 |
=0.025×999×2.8×40÷2.8,
=(0.025×40)×999×(2.8÷2.8),
=1×999×1,
=999;
③(
2 |
71 |
1 |
69 |
1 |
3 |
=
46 |
71 |
23 |
69 |
25 |
71 |
46 |
3 |
1 |
23 |
=(
46 |
71 |
25 |
71 |
23 |
69 |
2 |
3 |
=1-
23 |
69 |
2 |
3 |
=
69 |
69 |
23 |
69 |
46 |
69 |
=
82 |
69 |
④9.81×0.1+0.5×98.1+0.049×981,
=9.81×0.1+5×9.81+4.9×9.81,
=9.81×(0.1+5+4.9),
=9.81×10
=98.1;
⑤1000+999-998-997+996+995-994-993+…+104+103-102-101
=(1000+999-998-997)+(996+995-994-993)+…+(104+103-102-101)
=4+4+…+4
=4×(900÷4)
=4×900÷4
=900.
点评:根据题意,选择合适的计算方法进行简算,注意简算的各种变化.
练习册系列答案
相关题目