What is the difference between the average number of students of school A and B together and the average number of teachers of school C and D together?

In school A, Let number of students and teachers be 5x and 3x respectively. Now, 5x – 3x = 400 => x = 200 Total number of students = 5x = 1000 Total number of teachers = 3x = 600 Now, 2a = 1000 => a = 500 In school B, Let number of students and teachers be 7x and 9x respectively. Now, 9x – 7x = 320 => x = 160 Total number of students = 7x = 1120 Total number of teachers = 9x = 1440 Now, b + 340 = 1120 => b = 780 In school C, Here, m = 90 => n – m = 160   [n > m given] => n – 90 = 160 => n = 250 Total number of students = 90 Total number of teachers = 250 In school D, Let number of students and teachers be 4x and 5x respectively. Now, 5x – 4x = 100 => x = 100 Total number of students = 4x = 400 Total number of teachers = 5x = 500 Now, c² = 400 => c = 20 Average number of students of school A and B together = (1000 + 1120)/2 = 1060 Average number of teachers of school C and D together = (250 + 500)/2 = 375 Required difference = 1060 – 375 = 685