A psychic was tested for ESP. The psychic was presented with 400cards face down and was asked to determine if the card was one offour symbols: a cross, a star, a circle, or a square. The psychicwas correct in 120 of the cases. Let p represent the probabilitythat the psychic correctly identifies the symbol on the card in arandom trial.
A. Using the results above, construct a 99% confidence intervalfor p.
| a | (.255, .345) |
| b | (.262, .338) |
| c | (.241, .359) |
| d | (.259, .341) |
| e | We can assert that p = 0.25 with 100% confidence because thepsychic is just guessing. |
B. How large a sample n would you need to estimate p with amargin of error of 0.01 with 95% confidence? (Use the guess 0.25 asthe value of p)
| a | N = 447 |
| b | N = 7203 |
| c | N = 9604 |
| d | N = 30 |
