A merchant has coffee worth $20 a pound that she wishes to mix with 90 pounds of coffee worth $60 a pound to get a mixture that she will sell for $50 a pound. How many pounds (lb) of the $20 coffee should be used?

let x and 400 - x be the two numbers.  

==> 0.80x + 0.85(400 - x) = 400 - 68 from the statement of the problem.  

< ==> 0.80x + 0.85(400 - x) = 400 - 68  

==> 340 - 0.05x = 332  

< ==> -0.05x = -8 ==> x = 160, the first number ==> 400 - x = 240, the second number.

the answer on ed. is:

c. "the graph of f(x) has exactly two x-intercepts."

hope i could someone! : )

the formula of a midpoint between a abd b: