The equation of the parabola whose focus is at (0, 5) and directrix at y = -5 is:

y = (1/20)x²
y = -(1/20)x²
x = (1/20)y²

Aresearch study is done to find the average age of all u.s. factory workers. the researchers asked every factory worker in ohio what their birth year is. this research is an example of a census survey convenience sample simple random sample