一、口算。
$5.8 - 2.5 =$
$130 × 3 =$
$450 + 450 =$
$106 × 5 =$
$320 - 18 =$
$280 ÷ 70 =$
$12 + 1.26 =$
$270 ÷ 5 =$
$212 × 4 =$
$70 × 20 =$
$600 - 60 =$
$480 ÷ 8 =$
$6.82 - 6.2 =$
$30 × 600 =$
$240 ÷ 20 =$
$684 ÷ 2 =$
$0.78 + 0.5 =$
$420 × 20 =$
$15.1 + 4.9 =$
$80 × 51 =$
$575 ÷ 5 =$
$320 ÷ 8 =$
$15.6 - 10 =$
$14 × 300 =$
$4.73 - 1.64 =$
$20 × 27 =$
$0.91 + 0.31 =$
$3000 ÷ 600 =$
$20 - 4.2 =$
$580 ÷ 20 =$

$5.8 - 2.5 = 3.3$
$130 × 3 = 390$
$450 + 450 = 900$
$106 × 5 = 530$
$320 - 18 = 302$
$280 ÷ 70 = 4$
$12 + 1.26 = 13.26$
$270 ÷ 5 = 54$
$212 × 4 = 848$
$70 × 20 = 1400$
$600 - 60 = 540$
$480 ÷ 8 = 60$
$6.82 - 6.2 = 0.62$
$30 × 600 = 18000$
$240 ÷ 20 = 12$
$684 ÷ 2 = 342$
$0.78 + 0.5 = 1.28$
$420 × 20 = 8400$
$15.1 + 4.9 = 20$
$80 × 51 = 4080$
$575 ÷ 5 = 115$
$320 ÷ 8 = 40$
$15.6 - 10 = 5.6$
$14 × 300 = 4200$
$4.73 - 1.64 = 3.09$
$20 × 27 = 540$
$0.91 + 0.31 = 1.22$
$3000 ÷ 600 = 5$
$20 - 4.2 = 15.8$
$580 ÷ 20 = 29$

二、计算下面图形的底或高。
1.
2.

1. $84÷7=12(\mathrm{m})$
2. $28×2÷14=4(\mathrm{cm})$