Number of boys \\\\(= 70\\\\)Average marks of boys \\\\(=75\\\\)Total marks of boys \\\\(=70 \ imes 75=5250\\\\)Total marks of the class \\\\(=72 \ imes 100 =7200\\\\)Total marks of girls \\\\(=1950\\\\)Average of the girls \\\\(=\\dfrac{1950}{30}=65\\\\)