Answer: a. 1
Step-by-step explanation:
Given : Population mean :[tex]\mu=28\ cm[/tex]
Standard deviation : [tex]\sigma=1.3\ cm[/tex]
Let n be the number of times a beach ball with a diameter of 26.7 cm differ from the mean.
Then, we have
[tex]28-n(1.3)=26.7\\\\\Rightarrow\ 1.3n=28-26.7\\\\\Rightarrow\ 1.3 n=1.3\\\\\Rightarrow\ n=1[/tex]
Hence, a beach ball with a diameter of 26.7 cm is 1 standard deviation differ from the mean.