Just a Minute Solution:

lines = int(input())
sum_mins = 0
sum_secs = 0
for _ in range(lines):
    line_nums = list(map(int, input().split()))
    sum_mins += line_nums[0]
    sum_secs += line_nums[1]
measurement_minutes = sum_secs / 60 / sum_mins
if measurement_minutes > 1:
    print(measurement_minutes)
else:
    print("measurement error")