Using Chebysheff's theorm, you have concluded that at least 72.44% of the 2,924 runners took between 62.4 and 84.6 minutes to complete the 10km race. What was the standard deviation of these 2,924 runners?
Using 1-1/k^2 I can get the value of k correct. But then I struggle with the math to then get the standard deviation value correct. mean-k(sd)=LL doesn't seem to help me here.