Question 971405
Chebyshev's Theorem puts a bound on the percentage between x number of standard deviations. A certain amount of data must fall within 1-[1/(sd)^2], so at least 3/4 of people will be within two standard deviations.  It may be more, and it usually is, but it can not be fewer than 3/4.  

The data are mean +/- 2 sds or 75 to 155 minutes.  At least 75% of the runners finished in that time interval.