快点谢谢大家？

解一：57.35 -12.65-17.35等于27.35
因为有2个35可以合并：
=（57.35-17.35）-12.65
去小括号：
=40-12.65
=27.35
解二：9.8x5.2÷4.9等于10.4
因为9.8和4.9可以除的
（9.8÷4.9）x5.2

=2x5.2
=10.4
解三：12.5x4.8x0.3等于18
因为4.8可以做成（4x1.2）（8x0.6）（2x2.4）
=（12.5x4）x（1.2x0.3）

=50x0.36
=18
4.8还可以做8x0.6
=（12.5x8）x（0.6x0.3）
=100x0.18
=18

4.8可以做成2x2.4
=（12.5x2）x（2.4x0.3）
=25x0.72
0.72可以做成0.9x0.8
=（25x0.8）x0.9
=20x0.9
=18
解四：7.8x6.9+0.78x31等于78
因为6.9和31，7.8和0.78一样的，其中6.9和31可以变成69和31，
=（69+31）x0.78去括号
=100x0.78
=78

57.35-12.65-17.35
=(57.35-17.35)-12.65
=57.35-(12.65+17.35)
=27.35
9.8×5.2÷4.9
=9.8÷4.9×5.2
=2×5.2
=10.4
12.5×4.8×0.3
=12.5×8×0.6×0.3
=100×0.6×0.3
=18
7.8×6.9+0.78×31
=0.78×(69+31)
=0.78×100
=78

57.35-12.65-17.35
=57.35-(12.65+17.35)
=57.35-30
=27.35
9.8×5.2÷4.9
=9.8÷4.9×5.2
=2×5.2
=10.4
12.5×4.8×0.3
=(12.5×0.8）×(6×0.3)
=10×1.8
=18
7.8×6.9+0.78×31
=7.8×6.9+7.8×3.1
=7.8×(6.9+3.1)
=7.8×10
=78

57.35-12.65-17.35
=57.35-17.35-12.65
=40-12.65
=17.35
9.8x5.2÷4.9
=9.8÷4.9x5.2
=2x5.2
=10.4
12.5x4.8x0.3
=12.5x8x0.6x0.3
=100x0.18
=18
7.8x6.9+0.78x31
=0.78x69+0.78x31
=0.78x（69+31）
=0.78x100
=78