When bonding​ teeth, orthodontists must maintain a dry field. Anew bonding adhesive has been developed to eliminate the necessityof a dry field.​ However, there is concern that the new bondingadhesive is not as strong as the current​ standard, a compositeadhesive. Tests on a sample of 9 extracted teeth bonded with thenew adhesive resulted in a mean breaking strength​(after 24​ hours)of overbar x=5.78 Mpa and a standard deviation of s=0.41 Mpa.Orthodontists want to know if the true mean breaking strength isless than 6.35 ​Mpa, the mean breaking strength of the compositeadhesive.
A) We must assume that the sample was not random and selectedfrom a population with a highly skewed distribution.
B.)We must assume that the sample was random and selected from apopulation with a distribution that is approximately normal.
C.)We must assume that the sample was not random and selectedfrom a normally distributed population.
D).We must assume that the sample was random and selected from apopulation that is highly skewed.
