With higher unemployment rates for young adults, an raising number of parents are providing some form of financial support for their adult children. According to the 2013 Harris poll, parents of 18- to 35-year-old children spend average of $108 per month for their offspring's phone, music, video and remote Web services. Suppose the population standard deviation for this financial support is $33 per month. A random sample of 31 adults with the 18- to 35- year old children was chosen and was found to have average of $91 per month for this kind of financial support.
a. Does this sample provide support for conclusions of the Harris poll?
b. Determine the symmetrical interval that includes 95% of the sample means if the true population mean is $108 per month.