Let x and y be the number of boys and girls, respectively.
Given, mean marks (out of 100) of boys `(barx_(1))=70`
and mean marks (out of 100) of girls `(barx_(2))` =73
Also, given that, mean marks of all the students in the exmaination `(barx_(12))=71`
Now, using the formula,
Combined mean , `(barx_(12))= (barx_(1)n_(1)+barx_(2)n_(2))/(n_(1)+n_(2))=71` (Given)
`therefore (70n_(1) + 73n_(2))/(n_(1)+n_(2))=71`
`rArr 70n_(1)+73n_(2)= 71n_(1)+71n_(2)`
`rArr 73n_(2)-71n_(2)=71n_(1)-70n_(1)`
`rArr 2n_(2)=n_(1)`
`rArr n_(1)/n_(2)=2/1 or n_(1):n_(2)=2:1`
