1. 直接写出得数。
$8.6 - 3.5 =$ $2.4 + 0.9 =$ $2.5 - 1.72 =$
$12.34 + 5.67 =$ $420 ÷ 1000 =$ $80 × 0.7 =$
$17.2 - 5.8 - 4.2 =$ $125 × 8 ÷ 125 × 8 =$ $0.3 - 0.3 × 0.1 =$
$2.4 × 6 =$ $3.2 × 0.5 =$ $30 × 1.2 =$
$9^{2} =$ $4^{2} =$ $0.9 ÷ 100 =$
$0.26 + 2.6 =$ $9.9 + 1 =$ $5.28 - 0.8 =$

8.6 - 3.5 = 5.1
2.4 + 0.9 = 3.3
2.5 - 1.72 = 0.78
12.34 + 5.67 = 18.01
420 ÷ 1000 = 0.42
80 × 0.7 = 56
17.2 - 5.8 - 4.2 = 7.2
125 × 8 ÷ 125 × 8 = 64
0.3 - 0.3 × 0.1 = 0.27
2.4 × 6 = 14.4
3.2 × 0.5 = 1.6
30 × 1.2 = 36
9² = 81
4² = 16
0.9 ÷ 100 = 0.009
0.26 + 2.6 = 2.86
9.9 + 1 = 10.9
5.28 - 0.8 = 4.48

2. 解方程。
$x ÷ 2.5 = 5$ $3.7x - 1.7x = 58$
$x ÷ 17.6 = 12.4$ $x ÷ 0.6 = 3.5$
$2x = 11.5 - 3.5$ $x ÷ 7.1 = 39$
$2x = 14$ $1.6x - 0.6x = 12$
$1300 = 100x$ $0.4x + 5.6x = 36$

解：$x ÷ 2.5 × 2.5 = 5 × 2.5$
$x = 12.5$
解：$(3.7 - 1.7)x = 58$
$2x = 58$
$2x ÷ 2 = 58 ÷ 2$
$x = 29$
解：$x ÷ 17.6 × 17.6 = 12.4 × 17.6$
$x = 218.24$
解：$x ÷ 0.6 × 0.6 = 3.5 × 0.6$
$x = 2.1$
解：$2x = 8$
$2x ÷ 2 = 8 ÷ 2$
$x = 4$
解：$x ÷ 7.1 × 7.1 = 39 × 7.1$
$x = 276.9$
解：$2x ÷ 2 = 14 ÷ 2$
$x = 7$
解：$(1.6 - 0.6)x = 12$
$x = 12$
解：$100x ÷ 100 = 1300 ÷ 100$
$x = 13$
解：$(0.4 + 5.6)x = 36$
$6x = 36$
$6x ÷ 6 = 36 ÷ 6$
$x = 6$