A class of 85 students writing an exam had a mean mark of 74.2 write down the total sum of the 85 grades.

74.2 * 85

To find the total sum of the 85 grades, you need to multiply the mean mark by the number of students.

First, calculate the total sum by multiplying the mean mark (74.2) by the number of students (85):

Total sum = Mean mark * Number of students
Total sum = 74.2 * 85

Calculating this, we get:

Total sum = 6295

Therefore, the total sum of the 85 grades is 6295.