SOLUTION: can you help i keep getting a negative peanuts sell for three dollars a pound cashews sell for six dollars a pound how many pounds of cashews should be mixed with tweleve pound

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Question 717756: can you help i keep getting a negative
peanuts sell for three dollars a pound cashews sell for six dollars a pound how many pounds of cashews should be mixed with tweleve pounds of peanuts to obtain a mixture selling for four dollars and twenty cents a pound

Found 3 solutions by josgarithmetic, josmiceli, DrBeeee:
Answer by josgarithmetic(39799) About Me  (Show Source):
You can put this solution on YOUR website!
Price for peanuts, 3.00 $/#. Amount peanute = 12 #.
Price for cashews, 6.00 $/#. Amount is variable, c.
Target price for mixture = 4.00 $/#.

Fundamentally, cost divided by pounds is price per pound.
(cost)/(quantity)=(price)

highlight%28%2812%2A3%2Bc%2A6%29%2F%2812%2Bc%29=4%29. Solve for c.
..
.
highlight%28c=6%29, pounds of cashews.

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = pounds of cashews to be used
+6x+ = cost of cashews used
+3%2A12+=+36+ = cost of peanuts used
---------------
+%28+6x+%2B+36+%29+%2F+%28+x+%2B+12+%29+=+4.2+
+6x+%2B+36+=+4.2%2A%28+x+%2B+12+%29+
+6x+%2B+36+=+4.2x+%2B+50.4+
+1.8x+=+14.4+
+x+=+8+
8 pounds of cashews should be used
check answer:
+%28+6%2A8+%2B+36+%29+%2F+%28+8+%2B+12+%29+=+4.2+
+%28+48+%2B+36+%29+%2F+20+=+4.2+
+84%2F20+=+4.2+
+84+=+84+
OK

Answer by DrBeeee(684) About Me  (Show Source):
You can put this solution on YOUR website!
Knowns:
a) peanuts cost $3/lb
b) cashews cost $6/lb
c) mixture uses 12lb of peanuts
d) the mixture costs $4.20/lb
Unknown:
1) how many pounds of cashews are needed?
Let c = number of pounds of cashews
What relationship do we use get c?
"The cost of the peanuts plus the cost of the cashews equals the cost of the mixture", wherein the cost is the product of the cost per pound and the number of pounds. This relationship gives us the following equation,
(1) 3*12 + 6*c = 4.20*(12 + c) or
(2) 36 + 6*c = 50.4 + 4.2*c or
(3) 1.8*c = 14.4 or
(4) c = 8
Let's check this using (1).
Is (3*12 + 6*8 = 4.2*(12 + 8))?
Is (36 + 48 = 4.2*20)?
Is (84 = 84)? Yes
Answer: Use 8 pounds of cashews.