1. 直接写出得数。
$9.9 - 3.49 =$ $80 - 8.8 =$ $8.7 + 0.3 =$
$1.26 + 0.4 =$ $8.64 - 2.6 =$ $3 - 0.3 =$
$9.6 - 6.9 =$ $8.2 - 5.15 =$ $10 - 3.45 =$
$0 ÷ 21 =$ $0.4 × 99 + 0.4 =$ $50 × 0.25 =$
$35 × 0.2 =$ $0.5 + 0.75 + 0.25 =$ $1.2 × 0.6 =$

$9.9 - 3.49 = 6.41$
$80 - 8.8 = 71.2$
$8.7 + 0.3 = 9$
$1.26 + 0.4 = 1.66$
$8.64 - 2.6 = 6.04$
$3 - 0.3 = 2.7$
$9.6 - 6.9 = 2.7$
$8.2 - 5.15 = 3.05$
$10 - 3.45 = 6.55$
$0 ÷ 21 = 0$
$0.4 × 99 + 0.4 = 40$
$50 × 0.25 = 12.5$
$35 × 0.2 = 7$
$0.5 + 0.75 + 0.25 = 1.5$
$1.2 × 0.6 = 0.72$

2. 解方程。
$x + 3.46 = 17.5$ $x - 0.9 = 24.7$
$x ÷ 0.7 = 1.2$ $2x + 23 × 4 = 134$
$5x - 1.3 = 18.7$ $5.67 + 2x = 13.67$
$17x - 3 = 48$ $56 + 2x = 98$
$52x + 15x = 134$ $12x - 5.6 = 6.4$

解：$x + 3.46 = 17.5$
$x = 17.5 - 3.46$
$x = 14.04$
解：$x - 0.9 = 24.7$
$x = 24.7 + 0.9$
$x = 25.6$
解：$x ÷ 0.7 = 1.2$
$x = 1.2 × 0.7$
$x = 0.84$
解：$2x + 23 × 4 = 134$
$2x + 92 = 134$
$2x = 134 - 92$
$2x = 42$
$x = 42 ÷ 2$
$x = 21$
解：$5x - 1.3 = 18.7$
$5x = 18.7 + 1.3$
$5x = 20$
$x = 20 ÷ 5$
$x = 4$
解：$5.67 + 2x = 13.67$
$2x = 13.67 - 5.67$
$2x = 8$
$x = 8 ÷ 2$
$x = 4$
解：$17x - 3 = 48$
$17x = 48 + 3$
$17x = 51$
$x = 51 ÷ 17$
$x = 3$
解：$56 + 2x = 98$
$2x = 98 - 56$
$2x = 42$
$x = 42 ÷ 2$
$x = 21$
解：$52x + 15x = 134$
$67x = 134$
$x = 134 ÷ 67$
$x = 2$
解：$12x - 5.6 = 6.4$
$12x = 6.4 + 5.6$
$12x = 12$
$x = 12 ÷ 12$
$x = 1$