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2 answers:
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Group A
Money spent by Person 1 = £500
Money spent by Person 2 = £600
Money spent by Person 3 = £900
Money spent by Person 4 = £450
Sum of money spent by group A = £2,450
Average money spent by group A =
⇒ Average money spent by group A = £612.5
Group B
Money spent by Person 1 = £700
Money spent by Person 2 = £500
Money spent by Person 3 = £680
Money spent by Person 4 = £500
Sum of money spent by group B = £2,380
Average money spent by group B =
⇒ Average money spent by group B = £595
Hence, Group B had lower average spend.
Answer:
a) Standard error = 2
b) Range = (76.08, 83.92)
c) P=0.69
d) Smaller
e) Greater
Step-by-step explanation:
a) When we have a sample taken out of the population, the standard error of the mean is calculated as:
where n is te sample size (n=25) and σ is the population standard deviation (σ=10).
Then, the standard error of the classroom average score is 2.
b) The calculations for this range are the same that for the confidence interval, with the difference that we know the population mean.
The population standard deviation is know and is σ=10.
The population mean is M=80.
The sample size is N=25.
The standard error of the mean is σM=2.
The z-value for a 95% confidence interval is z=1.96.
The margin of error (MOE) can be calculated as:
Then, the lower and upper bounds of the confidence interval are:
The range that we expect the average classroom test score to fall 95% of the time is (76.08, 83.92).
c) We can calculate this by calculating the z-score of X=79.
Then, the probability of getting a average score of 79 or higher is:
The approximate probability that a classroom will have an average test score of 79 or higher is 0.69.
d) If the sample is smaller, the standard error is bigger (as the square root of the sample size is in the denominator), so the spread of the probability distribution is more. This results then in a smaller probability for any range.
e) If the population standard deviation is smaller, the standard error for the sample (the classroom) become smaller too. This means that the values are more concentrated around the mean (less spread). This results in a higher probability for every range that include the mean.