Necesito hacerlo con el desarrollo y la verdad es que no entiendo como hacerlo.

Identify a1 and r for the geometric sequence an= -256(-1/4) n-1

Thompson and thompson is a steel bolts manufacturing company. their current steel bolts have a mean diameter of 127 millimeters, and a variance of 36. if a random sample of 35 steel bolts is selected, what is the probability that the sample mean would differ from the population mean by greater than 0.5 millimeters? round your answer to four decimal places.

Which number completes the inequality? 2/3 < _ < 7/9