扬帆起航
$3200 ÷ 200 =$ $4200 ÷ 700 =$ $44 × 8 =$
$292 + 308 =$ $72 ÷ 4 =$ $2000 - 37 =$
$1260 ÷ 30 =$ $1.29 - 0.18 =$ $7 - 2.5 =$
$140 × 3 =$ $213 ÷ 3 =$ $420 + 160 =$

$3200÷200=16$
$4200÷700=6$
$44×8=352$
$292 + 308=600$
$72÷4=18$
$2000 - 37=1963$
$1260÷30=42$
$1.29 - 0.18=1.11$
$7 - 2.5=4.5$
$140×3=420$
$213÷3=71$
$420 + 160=580$

乘风破浪
$461 + 39 =$ $219 + 54 =$ $740 × 5 =$
$90 ÷ 6 =$ $2.5 + 4.2 =$ $2.4 - 1.8 =$
$86.2 + 14.8 =$ $175 + 35 =$ $1.05 - 0.08 =$
$0.6 + 3.45 =$ $100 ÷ 25 =$ $5.7 + 99 =$
$1 - 0.39 =$ $6.07 × 100 =$ $300 ÷ 15 =$
$7.8 + 2.2 =$ $5.8 - 5 =$ $360 + 640 =$
$90 ÷ 30 =$ $14.5 ÷ 100 =$ $1 - 0.92 =$
$1.92 + 15.17 =$ $42 × 8 =$ $0.7 + 0.94 =$

$461 + 39 = 500$
$219 + 54 = 273$
$740 × 5 = 3700$
$90 ÷ 6 = 15$
$2.5 + 4.2 = 6.7$
$2.4 - 1.8 = 0.6$
$86.2 + 14.8 = 101$
$175 + 35 = 210$
$1.05 - 0.08 = 0.97$
$0.6 + 3.45 = 4.05$
$100 ÷ 25 = 4$
$5.7 + 99 = 104.7$
$1 - 0.39 = 0.61$
$6.07 × 100 = 607$
$300 ÷ 15 = 20$
$7.8 + 2.2 = 10$
$5.8 - 5 = 0.8$
$360 + 640 = 1000$
$90 ÷ 30 = 3$
$14.5 ÷ 100 = 0.145$
$1 - 0.92 = 0.08$
$1.92 + 15.17 = 17.09$
$42 × 8 = 336$
$0.7 + 0.94 = 1.64$

圆满返航
1. 三个连续的单数，如果中间的数是$2a - 1$($a$为非 0 自然数)，那么另外两个单数分别是()和()。
2. 下列自然数中，可以表示成四个连续自然数的和的是()。
A. 37
B. 38
C. 39
D. 40
秘籍点拨 1. 相邻两个单数之间有什么关系？
2. 四个连续自然数的和有什么特点？
第74片

1. 2a-3；2a+1
2. B