1. 解比例和方程。
$5.4 + 2x = 8.6$
$2.5:5 = x:8$
$0.2 = 1 - \frac{x}{24}$
$x - \frac{3}{5}x = 12$
$1 + 25\%x = 3.75$
$\frac{1}{2}:x = \frac{4}{7}:4$
$\frac{x}{20} = 15\%$
$4×(x - 3.1) = 9.2$
$8x + 1.5×3 = 16.5$
$6x + 4x = 1.8×4$

解：2x = 8.6 - 5.4
2x = 3.2
x = 1.6
解：5x = 2.5×8
5x = 20
x = 4
解：$\frac{x}{24}$ = 1 - 0.2
$\frac{x}{24}$ = 0.8
x = 0.8×24
x = 19.2
解：$\frac{2}{5}$x = 12
x = 12÷$\frac{2}{5}$
x = 30
解：25%x = 3.75 - 1
0.25x = 2.75
x = 2.75÷0.25
x = 11
解：$\frac{4}{7}$x = $\frac{1}{2}$×4
$\frac{4}{7}$x = 2
x = 2÷$\frac{4}{7}$
x = $\frac{7}{2}$（或3.5）
解：x = 15%×20
x = 0.15×20
x = 3
解：x - 3.1 = 9.2÷4
x - 3.1 = 2.3
x = 2.3 + 3.1
x = 5.4
解：8x + 4.5 = 16.5
8x = 16.5 - 4.5
8x = 12
x = 1.5
解：10x = 7.2
x = 0.72

2. 脱式计算。（能简算的要简算）
$(0.25×1.25)×(0.8×4)$
$3.8×29 + 3.8$
$3.4×0.72 + 3.4×0.28$
$8×(1.25 + 0.9)$

(0.25×1.25)×(0.8×4)
=(0.25×4)×(1.25×0.8)
=1×1
=1
3.8×29 + 3.8
=3.8×(29+1)
=3.8×30
=114
3.4×0.72 + 3.4×0.28
=3.4×(0.72+0.28)
=3.4×1
=3.4
8×(1.25 + 0.9)
=8×1.25 + 8×0.9
=10 + 7.2
=17.2