Question 233474
R = 50 x – x2.  
C = 2x  +40.
R-C>0 IS THE PROFIT EQUATION.
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50X-X^2-(2X+40)>0
50X-X^2-2X-40>0
-X^2+48X-40>0
X^2-48X+40>0
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 
X=(48+-SQRT[-48^2-4*1*40])/2*1
X=(48+-SQRT[2,304-160)/2
X=(48+-SQRT2144)/2
X=(48+-46.3)/2
X=(48+46.3)/2
X=94.3/2
X=47.15 ANS.
THIS SAYS THAT AT LEAST 48 UNITS MUST BE SOLD TO HAVE A PROFIT.