解①1÷ (1+
3
4 )
=1÷
7
4
=
4
7 ；
②5
1
5 +2
2
3 -
4
15
=7
13
15 -
4
15
=7
3
5 ；
③2.8× 5.6+3.4×2
4
5 -280%
=2.8×（5.6+3.4-1）
=2.8×8
=22.4；
④2
1
3 ×12.5×
6
7 ×8
=（
7
3 ×
6
7 ）×（12.5×8）
=2×100
=200；
⑤ [1-0.8÷(
2
3 +
2
15 )]
=1-0.8÷0.8
=1-1
=0；
⑥
77
88 ×77
=
539
8 ；
⑦1 ÷[0.5×(2
1
4 +0.25)-
1
4 ]
=1÷[0.5×2.5-0.25]
=1÷[1.25-0.25]
=1÷1
=1；
⑧[4 -(1
5
6 -0.75)÷2
8
9 ]×2
2
7 × 2
2
7
=[4-
13
12 ×
9
26 ]× 2
2
7
=[4-
3
8 ]× 2
2
7
=
29
8 × 2
2
7
=
58
7 ；
⑨ (
6
7 -
7
9 )×63
=
6
7 ×63 -
7
9 ×63
=54-49
=5；
⑩ (4
5
9 ×
1
12 +31
4
9 ÷12)+[8
9
16 -(3
9
16 +4
4
5 )]
=（4
5
9 +31
4
9 ）×
1
12 +[ 8
9
16 -3
9
16 -4.8]
=36×
1
12 +[5-4.8]
=3+0.2
=3.2．