(5 points per question; maximum score 80 points for Quiz 2. You must show your work to get full credit.) 1. Jerry got a box full of colorful candy balls. There were 50 of them: 20 red, 10 green, 12 yellow and 8 blue. After shaking the box, he randomly selected 2 candy balls from the box. Whats the probability that the first one was blue and the second one was yellow? 2. Which activity could probabilities be computed using a Binomial Distribution? a. Flipping a coin a 100 times b. Throwing a die one hundred times c. The probability of getting a heart while playing card games d. Grades earned by 100 students on a statistics final exam 3. Many researchers have argued that the TB skin test is not accurate. Imagine that the TB skin test is only 70% accurate. Sarah is thinking about having the test. She got a test, and shows positive. The probability of Sarah actually having TB is a. 70% b. 35% c. 30% d. More information needed to calculate 4. In a normal distribution, __ percentage of the area under the curve is within one standard deviations of the mean? a. 68% b. 100% c. 95% d. It depends on the values of the mean and standard deviation 5. The mean of a standard normal distribution is: a. 0 b. 1.0 c. -1.0 d. 100 6. A normal distribution with a mean of 25 and standard deviation of 5. What is the corresponding Z score for an observation having a value of 10? 7. Consider a normal distribution with a mean of 25 and standard deviation of 4. Approximately, what proportion of the area lies between values of 17 and 33. a. 95% b. 68% c. 99% d. 50% 8. For a standard normal distribution, whats the probability of getting a positive number? a. 50% b. 95% c. 68% d. We cannot tell from the given information 9. For a normal distribution with a mean of 16 and standard deviation of 2, whats the probability of getting a number greater than 20? 10. Two-hundred students took a statistics class. Their professor creatively decided to give each of them their Z-score instead of their grade, assuming the student scores are normally distributed. Rachel got her Z-score of -0.01 She was wondering how well she did on the exam. a. It was very good, much better than almost all of the other students b. It was so-so, but still better than half of the students. c. It was not that good, but is near the average. d. It was very bad and was almost in the bottom of the class. 11. A researcher collected some data and they form a normal distribution with a mean of 10. Whats the probability of getting a positive number from this distribution? a. 25% b. 50% c. 75% d. We cannot tell from the given information 12. How do we calculate the standard error of the mean? a. Sample standard deviation divided by square root of sample size b. Square root of sample variance c. Square root of population variance d. Sample standard deviation divided by sample size 13. A researcher tries to compare grades earned on the first quiz by boys and girls. He randomly chooses 10 students from boys and 15 students from girls and calculates the confidence interval on difference between means. How many degrees of freedom will you get in this t distribution? 14. _________________refers to whether or not an estimator tends to overestimate or underestimate a parameter. ______________refers to how much the estimate varies from sample to sample. a. Bias; standard error b. Sample variability; Bias c. Mean; standard deviation d. Standard deviation; Mean 15. You read about a survey in a newspaper and find that 70% of the 250 people sampled prefer Candidate A. You are surprised by this survey because you thought that more like 50% of the population preferred this candidate. Based on this sample, is 50% a possible population proportion? 16. Which of the following appropriately describes standard error of the mean? a. b. c. d. Standard error is the square root of the variance of the population Standard error is the square root of the sample standard deviation Standard error is the standard deviation of the sampling distribution of the mean Standard error is a measure of population skewness