12又3/4÷1又1/5+5.25×5/6=?

=139x137/138+137x139/138
=139x137x2/138
=(138+1)(138-1)x2/138
=(138-1/138)x2
=276-1/69

12又3/4=51/4 1又1/5=6/5 相除=乘以倒数 51/4乘5/6=255/24
5.25=5又1/4=21/4 乘5/6=105/24 255/24+105/24=360/24=15
第2题不会了

都转换为分数计算就可以了
相当于51/4*5/6+21/4*5/6=5/6*72/4=15；
139*137/138+137*139/138=139/138*（137+1)/138=139/138;

15

1 解 ；原式=40/3÷6/5＋525/100×5/6
=40/3×5/6＋525/100×5/6
=（40/3＋525/100）×5/6
=（1.3＋5.25）×5/6
= 6.55×5/6
= 6.5
2 解； 原式= 139×138/139＋137×136/137
= 138＋136
= 274