I still need to practice these statistic problems before my exam. My exam is tomorrow which will be kind of these questions. So, please help me to understand more. Thanks a lot

3) Can one increase response rates for a mailed survey by contacting respondents ahead of time? A study designed to address this question compared 3 groups of subjects. The first group received a preliminary letter about the survey, the second group was phoned, while the third received no preliminary contact. A positive response was defined as returning the survey within 2 weeks. (from James E. Stafford, "Influence of preliminary contact on mail returns", Journal of Marketing Research). Intervention Response Preliminary Letter Phone Call None Yes 171 146 118 No 220 68 455 a. Find the probability that a randomly selected person received a preliminary letter. 171 b. Find the probability that a randomly selected person responded yes, given that he or she received a phone call. c. Find the probability that a person received a letter and responded no. 171+118/435-0.46.4% d. Find the probability that a person received a letter or responded no. 171+118/435=0.66 4) Suppose we know that the weight of male runners in the U.S. conform to a Normal distribution with a mean of 150 pounds and a standard deviation of 15 pounds. A runner is selected at random. a) What is the probability that the runner's weight is less than 135 pounds? 0.16 b) What is the probability that the runner's weight is between 140 and 160 pounds? 0.4901492 or 0.50 c) Find the weight that corresponds with the bottom 5% of runners (5th percentile). .05 d) Suppose a random sample of 10 runners is selected. What is the probability that the sample mean for the ten runners is less than 135 pounds? Would this be considered an unusual event? Explain. 5) Determine whether each of the following variables would best be modeled as continuous or discrete: a) The number of CDs owned by a student discrete outcome b) The length of a newborn baby Continous outcome At a county animal shelter, the probability that a stray dog will be adopted is 40%. Assume the probability of will be adopted? adoption follows the binomial distribution. If 5 dogs are in the shelter, what is the probability that at most two 4'.2=0.08 or 8%