. In an experiment comparing two weight loss plans, 100 subjects were randomly assigned to two groups, A and B. The mean weight loss in group A was 10 pounds with a standard deviation of 8 pounds and the mean weight loss in group B was 7 pounds with a standard deviation of 11 pounds. The distributions of weight loss are approximately normal.
a. What is the probability that a randomly selected person from group A lost weight?
b. What is the probability that a randomly selected person from group B gained weight?
c. If you were to randomly select 3 people from group A, what is the probability that they
lost a total of 25 pounds or more?
d. If you were to randomly select one person from each group, what is the probability that
the person from group B lost more weight?
e. What is the probability that a randomly selected person from group A lost at least 5 more
pounds than a randomly selected person from group B?
f. In parts c-e, what assumption did you have to make? Is it reasonable?
(a)
Let X shows the weight loss of a person is group A. The z-score for x = 0 is
The probability that a randomly selected person from group A lost weight is
(b)
Let Y shows the weight loss of a person is group B. The z-score for Y = 0 is
The probability that a randomly selected person from group B gained weight is
(c)
Let T= X+X+X
Here T has normal distribution with parameters as follows
and standard deviation
The z-score for T = 25 is
The probability that they lost a total of 25 pounds or more is
(d)
Let W =X -Y
Here we need to find the probability W < 0.
The distribution of W will be normal with mean
and standard deviation
The z-score for W=0 is
The probability that the person from group B lost more weight is
(e)
Let W =X -Y
Here we need to find the probability W >= 5.
The distribution of W will be normal with mean
and standard deviation
The z-score for W=0 is
The probability that a randomly selected person from group A lost at least 5 more pounds than a randomly selected person from group B
(f)
Assumption: Normal distribution
Because distribution of weight losses are normal.
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