加法交换律：a+b=b+a
加法结合律：(a+b)+c=a+(b+c)
乘法交换律：a×b=b×a
一、在括号里填上合适的数或字母
1. (a × b) × c = a × ((b) × c)
2. a + b = b + (a)
3. a × b = b × (a)
4. 125 × 7 × 8 = 7 × (125 × (8))
5. 28 + 56 + 72 = 56 + (28 + (72))
6. a + b + c = a + ((c) + b)
二、加法简便计算 (凑整百、整十)
54 + 80 + 120 + 446 =
700
117 + 280 + 120 =
517
273 + 107 + 93 =
473
172 + 30 + 228 + 70 =
500
48 + 84 + 16 + 52 =
200
73 + 160 + 40 + 27 =
300
248 + 238 + 52 =
538
132 + 312 + 88 =
532
148 + 71 + 29 + 152 =
400
228 + 149 + 51 =
428
三、乘法简便计算 (找朋友: 25和4, 125和8)
25 × 32 =
1600
25 × 11 × 4 =
1100
4 × 10 × 25 =
1000
8 × 14 × 125 =
14000
125 × 64 =
13000
2 × 8 × 50 =
800
125 × 24 =
7000
125 × 11 × 8 =
11000