一、口算。
58 - 26 =
0.4 + 1.8 =
3 × 61 =
420 ÷ 6 =
12 × 30 =
81 ÷ 27 =
140 × 4 =
320 ÷ 5 =
101 + 39 =
5.6 - 2.3 =
20 × 52 =
806 ÷ 2 =
840 ÷ 30 =
5.43 - 1.4 =
614 + 76 =
150 × 50 =
480 ÷ 16 =
954 ÷ 9 =
0.87 + 0.3 =
101 × 80 =
630 ÷ 15 =
3.2 - 0.25 =
6.75 + 1.25 =
125 × 32 =

58 - 26 = 32
0.4 + 1.8 = 2.2
3 × 61 = 183
420 ÷ 6 = 70
12 × 30 = 360
81 ÷ 27 = 3
140 × 4 = 560
320 ÷ 5 = 64
101 + 39 = 140
5.6 - 2.3 = 3.3
20 × 52 = 1040
806 ÷ 2 = 403
840 ÷ 30 = 28
5.43 - 1.4 = 4.03
614 + 76 = 690
150 × 50 = 7500
480 ÷ 16 = 30
954 ÷ 9 = 106
0.87 + 0.3 = 1.17
101 × 80 = 8080
630 ÷ 15 = 42
3.2 - 0.25 = 2.95
6.75 + 1.25 = 8
125 × 32 = 4000

二、计算下面各题，怎样简便就怎样计算。
$12.7+4.59+13.4$
$(720÷80+41)×77$
$243×27+257×27$
$312÷(2×13)÷3$
$7.3-2.38+23.6$
$1600÷[2×(25+15)]$

$12.7+4.59+13.4 = 30.69$
$(720÷80+41)×77 = 3850$
$243×27+257×27 = 13500$
$312÷(2×13)÷3 = 4$
$7.3-2.38+23.6 = 28.52$
$1600÷[2×(25+15)] = 20$