Question 1078772
<pre>I think you should use 2 unknowns:

{{{system(

matrix(2,7,

x,""+"",y,"",""="","",28,
0.14x,""+"",0.07y,"",""="","",0.09*28))}}}

Get rid of the decimals by moving them all 2 places to the right:

{{{system(

matrix(2,7,

x,""+"",y,"",""="","",28,
14x,""+"",7y,"",""="","",9*28))}}}

Now we can divide the second equation through by 7

{{{system(

matrix(2,7,

x,""+"",y,"",""="","",28,
2x,""+"",y,"",""="","",9*4))}}}

{{{system(

matrix(2,7,

x,""+"",y,"",""="","",28,
2x,""+"",y,"",""="","",36))}}}

Multiply the first equation through by -1
to eliminate the y's

{{{system(

matrix(2,7,

-x,""-"",y,"",""="","",-28,
2x,""+"",y,"",""="","",36))}}}

{{{matrix(1,7,

x,"","","",""="","",8)}}}

So we must use 8 ounces of the 14% 

Substitute x = 8 in 

{{{matrix(1,7,

x,""+"",y,"",""="","",28)}}}

{{{matrix(1,7,

8,""+"",y,"",""="","",28)}}}

{{{matrix(1,7,

y,"","","",""="","",20)}}}

And we must use 20 ounces of the 7%.

Edwin</pre>