The ratio of boys and girls among 520 students of class A and 930 students of class B is 7 : 6 and 16 : 15. respectively.  The ratio of girls to the total students combined for classes A & B is?

69 : 145

Class A  → B  :  G

                 7  :  6   = 13

                        ↓        ↓

                      ×40     ×40

                      240      520

Class B  →  B    :    G

                 16   :    15   = 31

                              ↓        ↓

                           ×30     ×30

                           450      930

Total girls in class A and Class B = 240 + 450 = 690

Total students in both classes = 520 + 930 = 1450

Required Ratio = 690  :  1450

                      =   69  :  145