The empirical rule states that in a normal distribution,
68% of data is within 1 std deviation of the mean
95% of data is within 2 std deviation of the mean
99.7% of data is within 3 std deviation of the mean
In this case 95% of the cases would be within two std deviations of the mean
mean - 8 and mean + 8
72 - 8 = 64 and 72 + 8 = 80
then 95% of the scores are between 64% and 80% on the test.
Answer:
Option B - 90 students at random during lunch
Step-by-step
An unbiased sample is defined as:
A sample is an unbiased sample if every individual or the element in the population has an equal chance of being selected.
Based on this, we can eliminate:
Option A) - It prevents non-eighth-graders of the school from being represented.
Option C) - Students in a hallway might take a particular class together/may be of the same grade. This gives them an unfair advantage.
Option D) - All students who are not in chorus are not represented in this set.
<span>W = event where white marble is drawn
B = event where black marble is drawn
The two events W and B are independent. This is because the marble taken out on the first draw is put back into the bag. Since W and B are independent, we can use this rule
P(W and B) = P(w)*P(B)
Use the rule to get
P(W and B) = P(W)*P(B)
P(W and B) = (1/2)*(1/4)
P(W and B) = (1*1)/(2*4)
P(W and B) = 1/8
1/8 is equivalent to 0.125. Use long division or a calculator
0.125 = 12.5% </span>
A. in 11 years it will be reduced to 858.99, in 10 it will be reduced to 1,073.
b. 43 years
