722.
1) 3,75+2 1/2 = 3,75+2,5=6,25=6 1/4= 25/4
2) 2 1/3 -1,875= 2 1/3 -1 7/8 = 2 8/24 -1 21/24 = 11/24
3) 25/4 : 11/24 = 25*24/(4*11) = 150/11
4) 2,75-1 1/2 =2,75-1,5=1,25=5/4
5) 8 1/8+1,5 =8 1/8 + 1 4/8 = 9 5/8 =77/8
6) 5/4 : 77/8 = 5*8/(4*77) = 10/77
7) 150/11 -10/77 = 1050/77 - 10/77 = 1040/77
8) 1040/77 :10/11 = 1040*11/(77*10) =104/7 = 14 6/7
724.
2(1+x) -5(2x-y) = 2*5*(3y-1)
6(5y-2) -2(4x-5) = 2*6*(8-2x)
2+2x-10x+5y = 30y-10
30y-12-8x+10= 96-24x
2-8x=30y-5y-10
30y -2 =96-16x
8x+25y = 12 ( *-2)
16x+30y = 98
-16x-50y= -24
16x+30y= 98 (сложим)
-20y= 74
8x+25y=12
y= -74/20
8x+25y=12
y= -3 14/20 = -3,7
x= (12-25y)/8
x=(12+3.7*25)/8=13,0625 = 13 1/16