The students of litchfield High school are in grades 9,10,11,12. Of the students , 1/4th are in 9th grade, 1/3rd are in 10th grade, 1/6th is in 11th grade and there are 300 in the 12th grade, how many students are there all together?

Riding on a school bus are 20 students in 9th grade, 10 in 10th grade, 9 in 11th grade, and 7 in 12th grade. Approximately what percentage of the students on the bus are in 9th grade?