Question 1201376
population mean is assumed to be 27,000 per year.
sample of 25 mexicans shows the sample mean to be equal to 20,000 with a sample standard deviation of 10,000.
the standard error is equal to the sample standard deviation divided by the sample size = 10,000 / sqrt(25) = 10,000 / 5 = 2000.
you would use the t-score for the test because your standard deviation is from the sample and not from the population.
because you are looking at the mean of a sample, the standard error is used rather than the standard deviation.
standard error = standard deviation / sqrt(sample size) = 2000 / sqrt(25) = 2000 / 5 = 400.
the t-score formula is t = (x - m) / s
t is the t-score
x is the sample meaan
m is the population  mean
s is the standard error.
t = (x - m) / becomes t = (30000 - 27000) / 400 = 7.5
the critical t-score with 24 degrees of freedom (number of degrees of freedom equals sample size minus 1) is equal to 2.796939498.
somce the test t-score is greater than the critical t-score, the results are significant and the conclusiomn is that the mean income is greater than 27,000.