Question 1089386
x, volume of the 5%
y, volume of the 10%
z, volume of the 15%


Converting the description into a system of equations:
{{{system(5x+10y+15z=8*20,x+y+z=20,x=y+z+2)}}}


Simplifying the system of equations:
{{{system(x+2y+3z=32,x+y+z=20,x-y-z=2)}}}


Matrix to begin:
{{{(matrix(3,4,
1,2,3,32,
1,1,1,20,
1,-1,-1,2)
)}}}
-


{{{(matrix(3,4,
0,1,2,12,
0,2,2,18,
1,-1,-1,2)
)}}}


{{{(matrix(3,4,
0,1,2,12,
0,1,1,9,
1,-1,-1,2)
)}}}


{{{(matrix(3,4,
1,-1,-1,2,
0,1,2,12,
0,1,1,9)
)}}}


{{{(matrix(3,4,
1,-1,-1,2,
0,1,2,12,
0,0,1,3
)
)}}}


{{{(matrix(3,4,
1,-1,0,5,
0,1,0,6,
0,0,1,3)
)}}}


{{{(matrix(3,4,
1,0,0,11,
0,1,0,6,
0,0,1,3)
)}}}


--

Finished solution:
{{{system(x=11,y=6,z=3)}}}