SOLUTION: C = 3n + 210 C = 10n How is the answer 10n?

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Question 1047208: C = 3n + 210
C = 10n
How is the answer 10n?

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
I'm guessing that +C+=+10n+ isn't
actually the answer.
I think that you are being given 2
equations:
(1) +C+=+3n+%2B+210+
(2) +C+=+10n+
Both of these can be true, but only for
1 value of +n+
------------------------------------
That is because they are straight lines which
can only intersect in 1 point.
Now I will find that point ( the solution )
-----------------
Substitute (2) into (1)
(1) +10n+=+3n+%2B+210+
(1) +7n+=+210+
(1) +n+=+30+ ( what they are looking for )
and also:
(2) +C+=+10%2A30+
(2) +C+=+300+
----------------
So, the point of intersection is ( 30, 300 )
Here is the plot of both lines:
+graph%28+400%2C+400%2C+-10%2C+100%2C+-60%2C+600%2C+3x+%2B+210%2C+10x+%29+