The ratio of the total number of students who come to school by car to the total number of students who come to school by bus is:

From above diagram ,
The total number of students who come to school by car is represented in pie chart = 70°
The total number of students who come to school by bus is represented in pie chart = 90°
Required ratio = 70° : 90° = 7 : 9 = 21 : 27