1. 1/4+Х=3/4
Х=3/4-1/4
Х=2/4=1/2
х-2/7=5/21
Х=5/21+6/21
Х=11/21
2. 1/3+у=7/12
у=7/12-4/12
у=3/12=1/4
4/5-z=1/4
16/20-5/20=z
z=11/20
3. y-8/20 =3/5
y=12/20-8/20
y=4/20=1/5
3/8-z=1/4
3/8-2/8=z
1/8=z
4. x-1 3/4= 2 1/5
X = 7/4 +11/5
X=35/20+44/20
X=79/20=3 19/20
X+1/3=2 1/5
X = 33/15-5/15
X=28/15=1 13/15