Answer:
Do you have the math exercices? I am sorry but I can just help in the subjects concerning math. It is been some time since I studied biology and other high-school subjects.
Answer:
62.17% probability that a randomly selected exam will require more than 15 minutes to grade
Step-by-step explanation:
Problems of normally distributed samples are 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.
In this problem, we have that:

What is the probability that a randomly selected exam will require more than 15 minutes to grade
This is 1 subtracted by the pvalue of Z when X = 15. So



has a pvalue of 0.3783.
1 - 0.3783 = 0.6217
62.17% probability that a randomly selected exam will require more than 15 minutes to grade
1 and 1/2x+3/4x=5/8
combine x's
1 and 1/2x=4/4x+2/4x=6/4x
6/4x+3/4x=5/8=9/4x
9/4x=5/8
multiply both sides by 8
18x=5
x=5/18
x=5/18 or aprox 0.277777777777