Answer:
65.45
Step-by-step explanation:
Zscore = (x - mean) / standard deviation
x = score
Percentage below C :
D = 18% ; F = 12%
Sum = 30%
Obtain the Zscore for the proportion below D
P(Z < 0.30) = -0.524
Hence, Zscore = -0.524
Put Zscore = -0.524 in the equation :
-0.524 = (x - 72) / 12.5
-0.524 * 12.5 = x - 72
-6.55 = x - 72
-6.55 + 72 = x
x = 65.45
To receive a grade of C or better, score must be atleast 65.45
Average speed = Total distance/Time
A = 550km/6.5hr
A = 84.6 km per hr