I have problem in finding out how the figure (2.069) is calculated in the question.
normally, we use 1.96 intervals for 95%.
how come we use degree of freedom and finding the figure (2.069)
It’s a small sample and the population’s standard deviation is unknown; under those circumstances, you use a t-statistic to construct the confidence interval, instead of a z-statistic.
Go to the t-table on p. 734. Look in the column labeled “p = 0.025”, and the row df = 23; there you will find the critical value of 2.069. Note that this table gives one-tail probabilities. You have two tails with p = 5% (= 0.05), which is the same as a one-tail probability of 2.5% (= 5% / 2 = 0.025). You have a sample size of 24, so 23 (= 24 − 1) degrees of freedom.
That’s a good one!
LOL!
Thanks
But do we have to memories the whole table to get the figure. It is difficult on the exam day
You don’t have to memorize any values from a t-table. If you need such a value, they’ll give you an excerpt of the table.