2/3×5+2/5×7+2/7×9+2/9×11=10/3+14/5+18/7+22/9=92/15+316/63=3512/315=
=11 47/315
75:(5+10*2)=3
(75:(5+10))*2=10
<span>(15*(40-40:4)):2=225</span>
15*(40-40):4:2=0
(15*40)-40:(4:2)=580
0,8 : 1 + 1/4 = 0,8 + 1/4 = 0,8 + 0,25 = 1,05
Или:
0,8 : 1 + 1/4 = 8/10 + 1/4 = 4/5 + 1/4 = 16/20 + 5/20 = 21/20 = 1 1/20
1. 8/12+7/19=1 2/57
2. 18/19-1 2/57=18/19-59/57=-5/57