Bottles of a popular cola drink are supposed to contain 300 ml of cola. There is some variation from bottle to bottle because the filling machinery is not perfectly precise. The distribution of the contents is normal with standard deviation of 3 ml. A student who suspects that the bottler is under-filling measures the contents of six bottles. The results are: 299.4 297.7 301.0 298.9 300.2 297.0

Is this convincing evidence that the mean contents of cola bottles is less than the advertised 300 ml?