What adds ups to 5 but multiplies to give you 12

X + y = 5
    xy = 12

x + y = 5
      y = -x + 5

                xy = 12
      x(-x + 5) = 12
  x(-x) + x(5) = 12
       -x² + 5x = 12
             - 12   - 12
-x² + 5x - 12 = 0
 x² - 5x + 12 = 0
x = 5 ± √25 - 48
                2
x = -5 ± √-23
           2
x = -5 ± 4.79i
            2
x = -5 + 4.79i    or    x = -5 - 4.79i
            2                              2
x = -2.5 + 2.395i   or    x = -2.5 - 2.395i
y = -2.5 - 2.395i   or    y = -2.5 + 2.395i

The two numbers that add up to 5 and multiply to 12 is -2.5 ± 2.395i, which is -2.5 + 2.395i and -2.5 - 2.395i.

The answer is Marco can pass out 15 cups that hold 2.5 ounces of juice.