A random variable X has a mean of 120 and a standard deviation of 15 a random variable Y has a mean of 100 and a standard deviat
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Focus has coordinates (0, a)
a = -3
Thus, 4a = 4(-3) = -12
Because a is negative, we know it will be a concave down or concave left parabola. Hence, A and D can be eliminated. And we know it has to be B because the directrix is the horizontal line y = 3. Hence, the equation of the parabola becomes:
or 
a = -3
Thus, 4a = 4(-3) = -12
Because a is negative, we know it will be a concave down or concave left parabola. Hence, A and D can be eliminated. And we know it has to be B because the directrix is the horizontal line y = 3. Hence, the equation of the parabola becomes: