Я считаю ответ таким : 9.99
20) 8/14=4/7; 7/63=1/9; 30/84=5/14; 34*12/3*17=8/1=8
(5 2/9y + 3 1/3) x 3 - 7 2/3y=(47/9y + 10/3) x 3 - 7 2/3y=
=47/9y*3 + 10/3* 3 - 7 2/3y==47/3у+10-7 2/3у=15 2/3у+10-7 2/3у=8у+10
<span>Если y=3 1/8
8*3 1/8+10=8*24/8+10=24+10=34
если y=1.4
8*1,4+10=11,2+10=21,2</span>
1) -3
2) 1,7
3) 8,6
4) -5,26
5) 0
6) -0,671
Ну а в дробях я дуб дубом)
А) 1/6 + 1/9 = 3/18 + 2/18 = 5/18
б) 2/9 + 5/6 = 4/18 + 15/18 = 19/18
в) 2/9 + 3/8 = 16/72 + 27/72 = 43/72
г) 2/10 + 6/15 = 6/30 + 12/30 = 18/30
д) 3/10 + 2/12 = 18/60 + 10/60 = 28/60
е) 5/12 + 4/15 = 25/60 + 16/60 = 41/60
ж) 3/4 + 5/18 = 27/36 + 15/36 = 42/36
з) 2/26 + 3/39 = 6/78 + 6/78 = 12/78
и) 7/34 + 5/51 = 21/102 + 10/102 = 15/102
к) 4/210 + 5/140 = 8/420 + 15/420 = 23/420
л) 7/450 + 8/180 = 14/900 + 40/900 = 54/900
м) 9/180 + 7/120 = 18/360 + 21/360 = 39/360