登录
五、用简便方法计算。
1. $5.9 + 59.9 + 599.9 + 5999.9 + 0.4$
2. $70.5 + 70.7 + 69.8 + 71.1 + 70.8 + 68.8$
1. $5.9 + 59.9 + 599.9 + 5999.9 + 0.4$
2. $70.5 + 70.7 + 69.8 + 71.1 + 70.8 + 68.8$
答案
1. $5.9+59.9+599.9+5999.9+0.4$
$=(5.9+0.1)+(59.9+0.1)+(599.9+$
$0.1)+(5999.9+0.1)$
$=6+60+600+6000$
$=6666$
2. $70.5+70.7+69.8+71.1+70.8+68.8$
$=(70+0.5)+(70+0.7)+(70-0.2)+$
$(70+1.1)+(70+0.8)+(70-1.2)$
$=(70×6)+(0.5+0.7-0.2+1.1+0.8-1.2)$
$=420+1.7$
$=421.7$
$=(5.9+0.1)+(59.9+0.1)+(599.9+$
$0.1)+(5999.9+0.1)$
$=6+60+600+6000$
$=6666$
2. $70.5+70.7+69.8+71.1+70.8+68.8$
$=(70+0.5)+(70+0.7)+(70-0.2)+$
$(70+1.1)+(70+0.8)+(70-1.2)$
$=(70×6)+(0.5+0.7-0.2+1.1+0.8-1.2)$
$=420+1.7$
$=421.7$
