3.The grade-point averages of 20 college seniors selected at random from a graduating class are as follows: 3.2, 1.9 ,2.7, 2.4, 2.8, 2.9, 3.8, 3.0, 2.5, 3.3, 1.8, 2.5, 3.7, 2.8, 2.0, 3.2, 2.3, 2.1, 2.5, 1.9 Calculate the standard deviation.