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扬帆起航
$1 - 0.6 - 0.4 =$
$10 - 3.7 - 5.3 =$
$4.9 - 0.9 + 6 =$
$7.6 + 1.4 + 2 =$
$1 - 0.6 - 0.4 =$
0
$14 - 8.7 - 1.3 =$4
$4.73 - 1.55 - 0.45 =$2.73
$10 - 3.7 - 5.3 =$
1
$10 - 2.67 =$7.33
$1 - 0.34 - 0.66 =$0
$4.9 - 0.9 + 6 =$
10
$3.4 + 3.4 - 6 =$0.8
$9.43 - 5.43 - 0.47 =$3.53
$7.6 + 1.4 + 2 =$
11
$14.5 - 2 + 7.5 =$20
$25.3 - 2.2 - 7.8 =$15.3
答案
1. $1 - 0.6 - 0.4$
$\begin{aligned}&=1 - (0.6 + 0.4)\\&=1 - 1\\&=0\end{aligned}$
2. $14 - 8.7 - 1.3$
$\begin{aligned}&=14 - (8.7 + 1.3)\\&=14 - 10\\&=4\end{aligned}$
3. $4.73 - 1.55 - 0.45$
$\begin{aligned}&=4.73 - (1.55 + 0.45)\\&=4.73 - 2\\&=2.73\end{aligned}$
4. $10 - 3.7 - 5.3$
$\begin{aligned}&=10 - (3.7 + 5.3)\\&=10 - 9\\&=1\end{aligned}$
5. $10 - 2.67 = 7.33$
6. $1 - 0.34 - 0.66$
$\begin{aligned}&=1 - (0.34 + 0.66)\\&=1 - 1\\&=0\end{aligned}$
7. $4.9 - 0.9 + 6$
$\begin{aligned}&=(4.9 - 0.9) + 6\\&=4 + 6\\&=10\end{aligned}$
8. $3.4 + 3.4 - 6$
$\begin{aligned}&=6.8 - 6\\&=0.8\end{aligned}$
9. $9.43 - 5.43 - 0.47$
$\begin{aligned}&=(9.43 - 5.43) - 0.47\\&=4 - 0.47\\&=3.53\end{aligned}$
10. $7.6 + 1.4 + 2$
$\begin{aligned}&=(7.6 + 1.4) + 2\\&=9 + 2\\&=11\end{aligned}$
11. $14.5 - 2 + 7.5$
$\begin{aligned}&=(14.5 + 7.5) - 2\\&=22 - 2\\&=20\end{aligned}$
12. $25.3 - 2.2 - 7.8$
$\begin{aligned}&=25.3 - (2.2 + 7.8)\\&=25.3 - 10\\&=15.3\end{aligned}$
答案依次为：0；4；2.73；1；7.33；0；10；0.8；3.53；11；20；15.3
$\begin{aligned}&=1 - (0.6 + 0.4)\\&=1 - 1\\&=0\end{aligned}$
2. $14 - 8.7 - 1.3$
$\begin{aligned}&=14 - (8.7 + 1.3)\\&=14 - 10\\&=4\end{aligned}$
3. $4.73 - 1.55 - 0.45$
$\begin{aligned}&=4.73 - (1.55 + 0.45)\\&=4.73 - 2\\&=2.73\end{aligned}$
4. $10 - 3.7 - 5.3$
$\begin{aligned}&=10 - (3.7 + 5.3)\\&=10 - 9\\&=1\end{aligned}$
5. $10 - 2.67 = 7.33$
6. $1 - 0.34 - 0.66$
$\begin{aligned}&=1 - (0.34 + 0.66)\\&=1 - 1\\&=0\end{aligned}$
7. $4.9 - 0.9 + 6$
$\begin{aligned}&=(4.9 - 0.9) + 6\\&=4 + 6\\&=10\end{aligned}$
8. $3.4 + 3.4 - 6$
$\begin{aligned}&=6.8 - 6\\&=0.8\end{aligned}$
9. $9.43 - 5.43 - 0.47$
$\begin{aligned}&=(9.43 - 5.43) - 0.47\\&=4 - 0.47\\&=3.53\end{aligned}$
10. $7.6 + 1.4 + 2$
$\begin{aligned}&=(7.6 + 1.4) + 2\\&=9 + 2\\&=11\end{aligned}$
11. $14.5 - 2 + 7.5$
$\begin{aligned}&=(14.5 + 7.5) - 2\\&=22 - 2\\&=20\end{aligned}$
12. $25.3 - 2.2 - 7.8$
$\begin{aligned}&=25.3 - (2.2 + 7.8)\\&=25.3 - 10\\&=15.3\end{aligned}$
答案依次为：0；4；2.73；1；7.33；0；10；0.8；3.53；11；20；15.3
乘风破浪
$23 + 4.12 + 5.88 =$
$54 + 7.5 + 2.5 =$
$2.5 + 3.6 + 7.5 =$
$6.81 + 5 + 2.19 =$
$45 + 0.03 + 0.97 =$
$4.31 + 3.9 + 5.69 =$
$8.4 + 25 + 1.6 =$
$7.03 + 0.8 + 2.97 =$
$23 + 3.9 + 6.1 =$
$23 + 4.12 + 5.88 =$
33
$7.46 + 0.12 + 2.54 =$10.12
$54 + 7.5 + 2.5 =$
64
$3.64 + 1.9 + 6.36 =$11.9
$2.5 + 3.6 + 7.5 =$
13.6
$4.06 + 0.5 + 15.94 =$20.5
$6.81 + 5 + 2.19 =$
14
$20 + 5.6 + 4.4 =$30
$45 + 0.03 + 0.97 =$
46
$7.83 + 2.17 + 6.3 =$16.3
$4.31 + 3.9 + 5.69 =$
13.9
$34.9 + 60 + 5.1 =$100
$8.4 + 25 + 1.6 =$
35
$56 + 20.3 + 29.7 =$106
$7.03 + 0.8 + 2.97 =$
10.8
$5.35 + 1.5 + 1.65 =$8.5
$23 + 3.9 + 6.1 =$
33
$16.34 + 4.81 + 5.19 =$26.34
答案
1.$23 + 4.12 + 5.88 $
$=23+(4.12 + 5.88)$
$=23 + 10$
$=33$
2.$7.46 + 0.12 + 2.54$
$ =(7.46 + 2.54)+0.12$
$=10 + 0.12$
$=10.12$
3.$54 + 7.5 + 2.5$
$ =54+(7.5 + 2.5)$
$=54 + 10$
$=64$
4.$3.64 + 1.9 + 6.36$
$ =(3.64 + 6.36)+1.9$
$=10 + 1.9$
$=11.9$
5.$2.5 + 3.6 + 7.5$
$ =(2.5 + 7.5)+3.6$
$=10 + 3.6$
$=13.6$
6.$4.06 + 0.5 + 15.94$
$ =(4.06 + 15.94)+0.5$
$=20 + 0.5$
$=20.5$
7.$6.81 + 5 + 2.19$
$ =(6.81 + 2.19)+5$
$=9 + 5$
$=14$
8.$20 + 5.6 + 4.4$
$ =20+(5.6 + 4.4)$
$=20 + 10$
$=30$
9.$45 + 0.03 + 0.97$
$ =45+(0.03 + 0.97)$
$=45 + 1$
$=46$
10.$7.83 + 2.17 + 6.3$
$ =(7.83 + 2.17)+6.3$
$=10 + 6.3$
$=16.3$
11.$4.31 + 3.9 + 5.69$
$ =(4.31 + 5.69)+3.9$
$=10 + 3.9$
$=13.9$
12.$34.9 + 60 + 5.1$
$ =(34.9 + 5.1)+60$
$=40 + 60$
$=100$
13.$8.4 + 25 + 1.6$
$ =(8.4 + 1.6)+25$
$=10 + 25$
$=35$
14.$56 + 20.3 + 29.7$
$ =56+(20.3 + 29.7)$
$=56 + 50$
$=106$
15.$7.03 + 0.8 + 2.97$
$ =(7.03 + 2.97)+0.8$
$=10 + 0.8$
$=10.8$
16.$5.35 + 1.5 + 1.65$
$ =(5.35 + 1.65)+1.5$
$=7 + 1.5$
$=8.5$
17.$23 + 3.9 + 6.1$
$ =23+(3.9 + 6.1)$
$=23 + 10$
$=33$
18.$16.34 + 4.81 + 5.19$
$ =16.34+(4.81 + 5.19)$
$=16.34 + 10$
$=26.34$
$=23+(4.12 + 5.88)$
$=23 + 10$
$=33$
2.$7.46 + 0.12 + 2.54$
$ =(7.46 + 2.54)+0.12$
$=10 + 0.12$
$=10.12$
3.$54 + 7.5 + 2.5$
$ =54+(7.5 + 2.5)$
$=54 + 10$
$=64$
4.$3.64 + 1.9 + 6.36$
$ =(3.64 + 6.36)+1.9$
$=10 + 1.9$
$=11.9$
5.$2.5 + 3.6 + 7.5$
$ =(2.5 + 7.5)+3.6$
$=10 + 3.6$
$=13.6$
6.$4.06 + 0.5 + 15.94$
$ =(4.06 + 15.94)+0.5$
$=20 + 0.5$
$=20.5$
7.$6.81 + 5 + 2.19$
$ =(6.81 + 2.19)+5$
$=9 + 5$
$=14$
8.$20 + 5.6 + 4.4$
$ =20+(5.6 + 4.4)$
$=20 + 10$
$=30$
9.$45 + 0.03 + 0.97$
$ =45+(0.03 + 0.97)$
$=45 + 1$
$=46$
10.$7.83 + 2.17 + 6.3$
$ =(7.83 + 2.17)+6.3$
$=10 + 6.3$
$=16.3$
11.$4.31 + 3.9 + 5.69$
$ =(4.31 + 5.69)+3.9$
$=10 + 3.9$
$=13.9$
12.$34.9 + 60 + 5.1$
$ =(34.9 + 5.1)+60$
$=40 + 60$
$=100$
13.$8.4 + 25 + 1.6$
$ =(8.4 + 1.6)+25$
$=10 + 25$
$=35$
14.$56 + 20.3 + 29.7$
$ =56+(20.3 + 29.7)$
$=56 + 50$
$=106$
15.$7.03 + 0.8 + 2.97$
$ =(7.03 + 2.97)+0.8$
$=10 + 0.8$
$=10.8$
16.$5.35 + 1.5 + 1.65$
$ =(5.35 + 1.65)+1.5$
$=7 + 1.5$
$=8.5$
17.$23 + 3.9 + 6.1$
$ =23+(3.9 + 6.1)$
$=23 + 10$
$=33$
18.$16.34 + 4.81 + 5.19$
$ =16.34+(4.81 + 5.19)$
$=16.34 + 10$
$=26.34$
圆满返航
一个等腰三角形的顶角是$50^{\circ}$。假设其中一个底角是$x^{\circ}$，那么用方程来求底角的度数。下列方程中正确的是(
A.$x + 50 = 180$
B.$2x + 50 = 180$
C.$2 × 50 + x = 180$
D.$2x - 50 = 180$
秘籍点拨 等腰三角形有几个顶角？有几个底角？
第70片
一个等腰三角形的顶角是$50^{\circ}$。假设其中一个底角是$x^{\circ}$，那么用方程来求底角的度数。下列方程中正确的是(
B
)。A.$x + 50 = 180$
B.$2x + 50 = 180$
C.$2 × 50 + x = 180$
D.$2x - 50 = 180$
秘籍点拨 等腰三角形有几个顶角？有几个底角？
第70片
答案
B
解析
等腰三角形有1个顶角和2个底角，且两底角相等。三角形内角和为180°，顶角50°，底角为x°，则方程为2x + 50 = 180。
