410万 - 270万 =
280万 + 340万 =
400 × 18 =
3400 ÷ 20 =
81亿 - 25亿 =
130万 + 570万 =
480 × 200 =
7600 ÷ 20 =
530万 + 360万 =
48亿 + 45亿 =
480 × 200 =
6700 ÷ 20 =
530万 - 360万 =
48万 + 45万 =
400 × 250 =
5700 ÷ 30 =
330万 - 90万 =
380万 + 260万 =
7200 ÷ 80 =
7200 ÷ 36 =
8100 ÷ 90 =

解析：这些题目主要考查了基本的算术运算，包括加减法、乘法和除法，涉及到的数有万、亿等单位。
答案：
$410\text{万} - 270\text{万} = 140\text{万}$
$280\text{万} + 340\text{万} = 620\text{万}$
$400 × 18 = 7200$
$3400 ÷ 20 = 170$
$81\text{亿} - 25\text{亿} = 56\text{亿}$
$130\text{万} + 570\text{万} = 700\text{万}$
$480 × 200 = 96000$
$7600 ÷ 20 = 380$
$530\text{万} + 360\text{万} = 890\text{万}$
$48\text{亿} + 45\text{亿} = 93\text{亿}$
$480 × 200 = 96000$ （与上面重复，如果确实是两个相同的题目，则答案相同）
$6700 ÷ 20 = 335$
$530\text{万} - 360\text{万} = 170\text{万}$
$48\text{万} + 45\text{万} = 93\text{万}$
$400 × 250 = 100000$
$5700 ÷ 30 = 190$
$330\text{万} - 90\text{万} = 240\text{万}$
$380\text{万} + 260\text{万} = 640\text{万}$
$7200 ÷ 80 = 90$
$7200 ÷ 36 = 200$
$8100 ÷ 90 = 90$

21 × 11 =
22 × 11 =
23 × 11 =
24 × 11 =
25 × 11 =
26 × 11 =
27 × 11 =
28 × 11 =
29 × 11 =
30 × 11 =
31 × 11 =
11 × 72 =
11 × 87 =
43 × 11 =
37 × 11 =
11 × 96 =
68 × 11 =
11 × 36 =
11 × 34 =
11 × 35 =
11 × 53 =

解析：本题考查多位数乘两位数的口算技巧，特别是与$11$相乘的规律。当一个数与$11$相乘时，可以将这个数拆分为两部分，分别与$1$和$10$相乘，然后将两个结果相加，或者利用分配律简化计算。但更直接的方法是观察与$11$相乘的数的每一位如何变化。例如，$21 × 11$，可以将$21$的十位和个位分别作为新数的百位和个位，十位则是原来两位数的十位和个位之和（如果和大于$10$，则向百位进位）。
答案：
$21 × 11 = 231$
$22 × 11 = 242$
$23 × 11 = 253$
$24 × 11 = 264$
$25 × 11 = 275$
$26 × 11 = 286$
$27 × 11 = 297$
$28 × 11 = 308$
$29 × 11 = 319$
$30 × 11 = 330$
$31 × 11 = 341$
$11 × 72 = 792$
$11 × 87 = 957$
$43 × 11 = 473$
$37 × 11 = 407$
$11 × 96 = 1056$
$68 × 11 = 748$
$11 × 36 = 396$
$11 × 34 = 374$
$11 × 35 = 385$
$11 × 53 = 583$

1800 ÷ 30 =
180 ÷ 30 + 120 =
540 ÷ 6 - 12 =
500 × 40 =
600 ÷ 50 + 99 =
120 ÷ 40 + 59 =
260 ÷ 13 + 45 =
120 ÷ 40 =
5100 ÷ 20 =
12 × 40 + 700 =
420 ÷ 7 × 50 =
70 × 60 ÷ 3 =
210 × 3 + 90 =
720 ÷ 8 + 90 =
120 ÷ 60 × 5 =
7 × 60 ÷ 30 =
21 × 30 - 9 =
280 ÷ 4 + 90 =
80 × 30 ÷ 12 =
70 × 90 ÷ 21 =
340 ÷ 17 × 30 =

解析：这些题目主要考查基础的数学运算，包括除法、乘法、加法和减法。
答案：
$1800÷ 30=60$
$180÷ 30+120=6+120=126$
$540÷ 6-12=90-12=78$
$500× 40=20000$
$600÷ 50+99=12+99=111$
$120÷ 40+59=3+59=62$
$260÷ 13+45=20+45=65$
$120÷ 40=3$
$5100÷ 20=255$
$12× 40+700=480+700=1180$
$420÷ 7× 50=60× 50=3000$
$70× 60÷ 3=4200÷ 3=1400$
$210× 3+90=630+90=720$
$720÷ 8+90=90+90=180$
$120÷ 60× 5=2× 5=10$
$7× 60÷ 30=420÷ 30=14$
$21× 30-9=630-9=621$
$280÷ 4+90=70+90=160$
$80× 30÷ 12=2400÷ 12=200$
$70× 90÷ 21=6300÷ 21=300$
$340÷ 17× 30=20× 30=600$