Exam (elaborations)
STA 2023 Elementary Statistics STA 2023 Final Exam Practice questions and Answers
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- Saint Petersburg College
STA 2023 Elementary Statistics
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Practice STA 2023 – Test #3 T1) Using tables find (-1.14<z<2.18)
2) Find P(z>1.75)
3) Find P(-1.12<z<2.91)
4) Find P(z<-2.13)
5) Find P(X<150), when σ=17 and μ=147
6) During the month of July, the average temperatures in Tampa is 94⁰. The standard
deviation is 6⁰. Assume the variable is normally distributed. What is the probability for a
randomly selected day in July that the temperature will be between 90⁰ and 94⁰?
7) An average price of a new TV is $750. The laptop prices are normally distributed
and σ=$150. The least expensive 20% of the TV cost less than what amount?
8)A company produces a specific type of steel rod that is 112.4 cm long. The
standard deviation is 5.43 cm. Between what two values do 95% of the rod lengths lie?
Assume normal distribution.
9) The average salary for a teacher in a large city is $47,000. The standard deviation
is $4090. The salaries are normally distributed. What is the probability that a professor
chosen at random makes less than $45000?
10) The average annual household incomes in Georgia is $48175. Assume that the
incomes are normally distributed with a standard deviation of $2175. Find the
probability that a randomly selected household has an income greater than $47000?
11) The average cost of a new TV is $775 with a standard deviation of $125. What is
the probability that a TV selected at random cost more than $900?
12) The average annual household incomes in Georgia is $48175. Assume that the
incomes are normally distributed with a standard deviation of $2175. If a sample of 1000
households are selected, find the probability that a randomly selected household have an
income between $46000 and $49000
13)Find the 90% confidence interval about the mean for the life of lightbulbs (in
hours) where the average life is 1231.5 hours with a standard deviation of 121.7 from a
sample of size 250.
14)A sample of 12 students have an average grade in a trig class of 75 with a standard
deviation of 8. Find a 95% confidence interval about the mean for the average test grade
15)A survey is taken of 1000 registered voters. It is found that 725 favor Proposition
123 an upcoming election. Find a 95% confidence interval for the true mean proportion
of voters favoring Proposition 123
16) If we increased the confidence level in 15) to 99%, what would happen to the
confidence interval?
17) A sample of 19 kindergarten students have an average age of 5.3 years with a
standard deviation of .5 years. Construct a 95% confidence interval about the true mean
average age for a kindergartner.
18) What does changing the sample size do to a Confidence Interval? What does
changing the confidence level do to a Confidence Interval?
19)With a 99% confidence level, how large a sample should be chosen, if a
preliminary poll showed that 52% of votes favor a referendum. We wish to show this
within a 2% margin of error.
20) What would the sample size in 19) be if you had no preliminary information?
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