一、解方程。(带※的要写出检验过程)
$x - 35.6 = 57.5$
$45.3 + x = 66.2$
$3(x - 2.5) = 24$
$2x + 7x + 10 = 17.2$
※$(4x - 5)×5 = 25$

x=93.1 x=20.9 x=10.5 x=0.8 x=2.5(检验略)

x - 35.6 = 57.5
x = 57.5 + 35.6
x = 93.1
45.3 + x = 66.2
x = 66.2 - 45.3
x = 20.9
3(x - 2.5) = 24
x - 2.5 = 24 ÷ 3
x - 2.5 = 8
x = 8 + 2.5
x = 10.5
2x + 7x + 10 = 17.2
9x + 10 = 17.2
9x = 17.2 - 10
9x = 7.2
x = 7.2 ÷ 9
x = 0.8
※(4x - 5)×5 = 25
4x - 5 = 25 ÷ 5
4x - 5 = 5
4x = 5 + 5
4x = 10
x = 10 ÷ 4
x = 2.5
检验：把x = 2.5代入原方程，
左边 = (4×2.5 - 5)×5 = (10 - 5)×5 = 5×5 = 25，
右边 = 25，
左边 = 右边，
所以x = 2.5是原方程的解。

1. 当$x$等于()时,$3x + 9 = 24$。
A.2
B.5
C.15
D.11

B

解：$3x + 9 = 24$
$3x = 24 - 9$
$3x = 15$
$x = 5$
B

2. 与方程$3x - 6 = 21$的解相同的方程是()。
A.$20x = 19$
B.$2x = 18$
C.$4x - 16 = 24$
D.$3x = 18$

B

解方程$3x - 6 = 21$，得$3x=27$，$x=9$。
A. 解方程$20x = 19$，得$x=\frac{19}{20}\neq9$。
B. 解方程$2x = 18$，得$x=9$。
C. 解方程$4x - 16 = 24$，得$4x=40$，$x=10\neq9$。
D. 解方程$3x = 18$，得$x=6\neq9$。
B

三、看图列方程,并求出方程的解。
1.

2.
]

1. 3x+4.2=17.4 x=4.4 2. 5x-80=370 x=90

1. $3x + 4.2 = 17.4$
$3x = 17.4 - 4.2$
$3x = 13.2$
$x = 4.4$
2. $5x - 80 = 370$
$5x = 370 + 80$
$5x = 450$
$x = 90$

四、已知$a + b = 4.5,a + a + b = 6,a和b$的值分别是多少?

a+4.5=6,a=1.5 1.5+b=4.5 b=3

因为$a + b = 4.5$，所以$a + a + b = a + (a + b) = a + 4.5$。又因为$a + a + b = 6$，所以$a + 4.5 = 6$，解得$a = 6 - 4.5 = 1.5$。将$a = 1.5$代入$a + b = 4.5$，得$1.5 + b = 4.5$，解得$b = 4.5 - 1.5 = 3$。所以$a = 1.5$，$b = 3$。