CALCULATION:Total number of students from school A⇒ 640 + 800 + 500 + 700 + 900 + 750⇒ 4290Total number of students from school B⇒ 550 + 820 + 600 + 750 + 500 + 480⇒ 3700Ratio of average of total students from school A to school B⇒ (4290/6) : (3700/6)⇒ 4290 : 3700⇒ 429 : 370∴ The required RATIO is 429 : 370