Answer:
54
Step-by-step explanation:
![\frac{4}{3} \pi r^{3} =12\pi \\r=\sqrt[3]{9} \\surface area 4\pi r^{2} = 4\pi (\sqrt[3]{9} )^2=54.372 (3dp)](https://tex.z-dn.net/?f=%5Cfrac%7B4%7D%7B3%7D%20%5Cpi%20r%5E%7B3%7D%20%3D12%5Cpi%20%5C%5Cr%3D%5Csqrt%5B3%5D%7B9%7D%20%5C%5Csurface%20area%204%5Cpi%20r%5E%7B2%7D%20%3D%204%5Cpi%20%28%5Csqrt%5B3%5D%7B9%7D%20%29%5E2%3D54.372%20%283dp%29)
You made the choice to choose the letter A, a second time.
the whole exam will be 100%, and let's say that's "x" questions, but we also know that 9 is 60% of that so

Answer:
a) The mean is 
b) The standard deviation is 
Step-by-step explanation:
Normal Probability Distribution:
Problems of normal distributions can be solved using the z-score formula.
In a set with mean
and standard deviation
, the zscore of a measure X is given by:

The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.
The probability a student selected at random takes at least 55.50 minutes to complete the examination equals 0.6915.
This means that when X = 55.5, Z has a pvalue of 1 - 0.6915 = 0.3085. This means that when 
So




The probability a student selected at random takes no more than 71.52 minutes to complete the examination equals 0.8997.
This means that when X = 71.52, Z has a pvalue of 0.8997. This means that when 
So




Since we also have that 





Question
The mean is 
The standard deviation is 