Gerbils can develop gastrointestinal tract issues as they get older that may cause severe diarrhea and dehydration from the diarrhea. A researcher wishes to conduct a study to find which of two antibiotics, antibiotic a or antibiotic b, is more effective in improving gastrointestinal tract health. A total of 300 gerbils that are at least one year old will be randomly selected from zoos in the state of Florida. The researcher will get consent from all owners, treat the gerbils for 10 months and evaluate changes in gastrointestinal health.

part a: how would the study benefit from adding a control group?
part b: what is the best way to randomly place the gerbils into the antibiotic a, antibiotic b, and control groups?
part c: The researcher wants to use a blocking variable to place gerbils into groups instead of doing it randomly. He decides to block either by breed or zoo. Explain which would be the best blocking method.

An annual marathon covers a route that has a distance of approximately 26 miles. winning times for this marathon are all over 2 hours. the following data are the minutes over 2 hours for the winning male runners over two periods of 20 years each. earlier period 14 12 15 22 13 10 19 13 9 14 20 18 16 20 23 12 18 17 6 13 recent period 7 11 7 14 8 9 11 14 8 7 9 8 7 9 9 9 9 8 10 8 (a) make a stem-and-leaf display for the minutes over 2 hours of the winning times for the earlier period. use two lines per stem. (use the tens digit as the stem and the ones digit as the leaf. enter none in any unused answer blanks. for more details, view how to split a stem.) minutes beyond 2 hours earlier period 0 1 2 (b) make a stem-and-leaf display for the minutes over 2 hours of the winning times for the recent period. use two lines per stem. (use the tens digit as the stem and the ones digit as the leaf. enter none in any unused answer blanks.) minutes beyond 2 hours recent period (c) compare the two distributions. how many times under 15 minutes are in each distribution