After measuring the speed of sound u several times, a student concludes that the standard deviation of u of her measurements is sigma_u = 10 m/s. if all uncertainties were random, she could get any desired precision by making enough number of measurement and averaging. how many measurements are needed to have the final uncertainty of the speed of sound plusminus 3 m/s ? how many measurements are needed to have the final uncertainty of the speed of sound plusminus 0.3 m/s ?