Question 1047208
I'm guessing that {{{ C = 10n }}} isn't
actually the answer.
I think that you are being given 2
equations:
(1) {{{ C = 3n + 210 }}}
(2) {{{ C = 10n }}}
Both of these can be true, but only for
1 value of {{{ n }}}
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That is because they are straight lines which
can only intersect in 1 point.
Now I will find that point ( the solution )
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Substitute (2) into (1)
(1) {{{ 10n = 3n + 210 }}}
(1) {{{ 7n = 210 }}}
(1) {{{ n = 30 }}} ( what they are looking for )
and also:
(2) {{{ C = 10*30 }}}
(2) {{{ C = 300 }}}
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So, the point of intersection is ( 30, 300 )
Here is the plot of both lines:
{{{ graph( 400, 400, -10, 100, -60, 600, 3x + 210, 10x ) }}}