Subject :IMO Class : Class 9

The average marks (out of 100) of boys and girls in an examination are 70 and 73 respectively. If the average marks of all the students in an examination is 71, then find the ratio of the number of boys to the number of girls.
(A) 1 : 3
(B) 2 : 1
(C) 1 : 2
(D) 3 : 1