Answer:
To find the median marks, we need to arrange the marks in ascending order and find the middle value.
0-20: 42 students
21-30: 38 students
31-40: 120 students
41-50: 84 students
51-60: 48 students
61-70: 36 students
71-80: 32 students
Since there are a total of 450 students, the median will be the value at the 225th position if we arrange the marks in ascending order. The value at the 225th position will be the lower value of the interval that the 225th student falls in.
The students in the intervals 0-20, 21-30, and 31-40 account for 42+38+120 = 200 students, which means that the 25th student falls in the 41-50 interval. Therefore, the median marks are 41.5.
To find the percentage of failures, we need to count the number of students who scored below 35 marks and divide it by the total number of students, and multiply the result by 100 to express it as a percentage. The number of students who scored below 35 marks is 42+38 = 80. The percentage of failures is 80/450 * 100 = 17.78%.