Given the following frequency distribution for n = 100. Class intervals Frequency 0-under 10 30 a. Approximate the mean. 10-under 20 10 b. Approximate the standard deviation. 20-under 30 20 30-under 40 30 40-under 50 10 100 . . . . . a. X= (Type an integer or a decimal.) b. S= (Round to two decimal places as needed.)