Having done poorly on a particular exam in a junior high school, 21 students decide to write the exam again to try and improve their mark. Results are given in the following table. Student n Average Standard deviation Attempt 1 (A1) 21 52 3.0 Attempt 2 (A2) 21 56 4.9 Difference (d : A1 - 21 4.0 2.5 2) (a) Find a 95% confidence interval for the difference in mean scores between attempt 1 and attempt 2. (Round your answers to 4 decimal places, if needed.) (b) Based on this confidence interval, can we conclude there is a difference in mean scores between attempt 'l and attempt 2? O No, since the interval is completely below 0. 0 Yes, since the interval is completely below 0. 0 Yes, since the interval contains 0. O No, since the interval contains 0. Check