Answer:
The standard deviation of the sample mean is  [tex]\sigma _ {\= x } = 2.711[/tex]
Step-by-step explanation:
From the question we are told that
  The mean is  [tex]\= x = 60[/tex]
  The standard deviation is  [tex]\sigma = 21[/tex]
   The sample size is [tex]n = 60[/tex]
Generally the standard deviation of the sample mean is mathematically represented as Â
        [tex]\sigma _ {\= x } = \frac{\sigma }{\sqrt{n} }[/tex]
substituting values
        [tex]\sigma _ {\= x } = \frac{ 21 }{\sqrt{60} }[/tex]
        [tex]\sigma _ {\= x } = 2.711[/tex]
