A group of students measured the average monthly temperature of 1000 cities around the world and plotted the cumulative frequency graph shown below. A cumulative frequency graph. The label for the x-axis reads 'Average monthly temperature (in degrees Celsius).' The label for the y-axis reads 'Cumulative Frequency (number of cities).' The coordinates that make up the shape of the line are as follows: (0,0), (10,50), (20,50), (30,400), (40,700), (50,950), (60,1000), (70,1000).

Which of these conclusions is correct about the cities whose temperatures were measured by the students?