Among all the income-tax forms filed in a certain year, the mean tax paid was $2000 and the standard deviation was $500. In addition, for 10% of the forms, the tax paid was greater than $3000. A random sample of 625 tax forms is drawn. a. What is the probability that the average tax paid on the sample forms is greater than $1980? b. What is the probability that more than 60 of the sampled forms have a tax of greater than $3000?

Ch. 3 Statistical Descriptions of Data • Measures of Central Tendency & Dispersion: these show the center and variability and are calculated for numerical summaries • Measures of Central Tendency: describe the typical values of the data o Show the center of gravity/middle of the data • Mean (Average): add all the values and then divide by the number of values o Sample Mean: sum of the observations divided by the sample size (n) ̅ o A bar over a letter means the average, so X means the average of all values of X Σx o Equation: X= i n o The mean is not resistant to outliers; outliers will sway the mean •