52.8 minutes
Since it’s an estimate choose a midpoint of each category to represent its time value
15 min for 0-30 min group
45 min for 30-60
75 min for 60-90
105 min for 90-120
Then multiply the time for each group by the number of students and add together
15x7+45x27+75x12+105x4 = 2640 minutes
Then divide by the total number of students 50
2640/50=52.8 minutes
