To find the daily production number that yields a minimum cost, we need to find the value of x that minimizes the cost function C(x) = 800 - 50x + 0.25x^2.
We can find the minimum point of the quadratic function by using the formula:
x = -b/(2a)
where a = 0.25, b = -50.
Substituting these values into the formula, we get:
x = -(-50)/(2*0.25)
x = 100
Therefore, the daily production number that yields a minimum cost is 100 fixtures.