a+b=5/6 suy ra 2a+2b=2×5/6
suy ra 2a+2b=5/3(1)
b+c=7/12 suy ra 2b+2c=2×7/12
suy ra 2b+2c=7/6(2)
a+c=3/4
Lấy (1)-(2)
2a+2b-(2b+2c)=5/3-7/6
2a+2b-2b-2c=10/6-7/6
2a-2c=3/6
2×(a-c)=1/2
a-c=1/4
Do đó
a=(1/4+3/4):2=1/2
c=3/4-1/2=1/4
b=7/12-1/4=7/12-3/12=4/12=1/3