SOLUTION: Three varieties of coffee-Coffee A, Coffee B, and Coffee C-are combined and roasted, yielding a 55-lb batch of coffee beans. Twice as man pounds of Coffee C, which retails for $10.

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: Three varieties of coffee-Coffee A, Coffee B, and Coffee C-are combined and roasted, yielding a 55-lb batch of coffee beans. Twice as man pounds of Coffee C, which retails for $10.      Log On


   



Question 683962: Three varieties of coffee-Coffee A, Coffee B, and Coffee C-are combined and roasted, yielding a 55-lb batch of coffee beans. Twice as man pounds of Coffee C, which retails for $10.19 per lb, are needed as Coffee A, which sells for $15.21 per lb. Coffee B retails for $12.99 per lb. How many pounds of each coffee should be used in a blend that sells for $12.61 per lb
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +a+ = pounds of coffee A needed
Let +b+ = pounds of coffee B needed
Let +c+ = pounds of coffee C needed
given:
(1) +c+=+2a+
(2) +a+%2B+b+%2B+c+=+55+
(3) +%28+15.21a+%2B+12.99b+%2B+10.19c+%29+%2F+55+=+12.61+
--------------------------------------------
Multiply both sides of (3) by +100+
(3) +%28+1521a+%2B+1299b+%2B+1019c+%29+%2F+55+=+1261+
(3) ++1521a+%2B+1299b+%2B+1019c++=+69355+
Multiply both sides of (2) by +1019+ and
subtract (2) from (3)
(3) +1521a+%2B+1299b+%2B+1019c+=++69355+
(2) ++-1019a+-+1019b+-+1019c+=+-56045+
+502a+%2B+280b+=+13310+
+280b+=+13310+-+502a+
+b+=+1331%2F28+-+%28+251%2F140+%29%2Aa+
Plug this into (2)
(2) +a+%2B+b+%2B+c+=+55+
(2) +a+%2B+1331%2F28+-+%28+251%2F140+%29%2Aa+%2B+2a+=+55+
(2) +3a+-+%28+251%2F140+%29%2Aa++=+55+-++1331%2F28+
(2) +a%2A%28+3+-+1.7929+%29+=+55+-+47.5357+
(2) +1.2071a+=+7.4643+
(2) +a+=+6.1837+
and, since
(1) +c+=+2a+
(1) +c+=+2%2A6.1837+
(1) +c+=+12.3673+
and
(2) +a+%2B+b+%2B+c+=+55+
(2) +6.1837+%2B+b+%2B+12.3673+=+55+
(2) +b+=+55+-+6.1837+-+12.3673+
(2) +b+=+55+-+18.5510+
(2) +b+=+36.449+
6.1837 pounds of coffee A are needed
36.449 pounds of coffee B are needed
12.3673 pounds of coffee C are needed
---------------------------------
check:
(2) +a+%2B+b+%2B+c+=+55+
(2) +6.1837+%2B+36.449+%2B+12.3673+=+55+
(2) +55+=+55+
and
(3) +%28+15.21a+%2B+12.99b+%2B+10.19c+%29+%2F+55+=+12.61+
(3) +%28+15.21%2A6.1837+%2B+12.99%2A36.449+%2B+10.19%2A12.3673+%29+%2F+55+=+12.61+
(3) ++94.0541+%2B+473.4725+%2B+126.0228+=+55%2A12.61+
(3) +693.5494+=+693.55+
close enough