Randomly select classes.

(I) let * * draw n students, n60 = 16, ∴n= 10, that is, * * draw 10 students. ... (4 points)

(II) The histogram of frequency distribution from 2+4+x+ 1= 10, x=3 is as follows:

㈢。 X = 0.2× 5+0.4×15+0.3× 25+0.1× 35 = 18, so it is estimated that the average study time of this class is18 hours ... (12 minutes.