Using statement I
Let the total students in the class be \(x\)
Male in the class \(=(\frac{60}{100}) \times x=\frac{3x}{5}\)
Females in the class \(=(\frac{40}{100}) \times x=\frac{2x}{5}\)
Let the average weight of female students be \(y\)
Then, the average weight of male students \(=y+15\)
Sum of the weight of male students \(=(\frac{3x}{5}) \times(y+15)=\frac{3xy}{5}+9 x\)
Sum of the weight of female students \(=(\frac{2x}{5})\times y=\frac{2xy}{5}\)
\(\therefore\) Average weight of the class \(=\frac{(\frac{3xy}{5}+9 x+\frac{2xy}{5})}{x}=\frac{(x y+9 x)}{x}=y+9\)
New average of the class \(=y+9+0.84=y+9.84 \quad \ldots\) (i)
Statement I alone is not sufficient to answer the question.
Using statement II
Total male students in the class is \(12\) more than female students.
\(\therefore\) If number of female students \(=x\)
Then, number of male students \(=x+12\)
Let average weight be male students be \(y\)
\(\therefore\) New average weight of male \(=y+1\)
Average weight of female students be \(z\)
\(\therefore\) New average weight of female \(=z+0.6\)
Statement II alone is not sufficient to answer the question.
Using statement I and statement II together,
Total male students in the class is \(12\) more than female students
\(\Rightarrow(\frac{3x}{5})-(\frac{2x}{5})=12\)
\(x=60\)
\(\therefore\) Male students \(=\frac{3x}{5}=\frac{180}{5}=36\)
Female students \(=\frac{2x}{5}=\frac{120}{5}=24\)
Avg weight of female and male students is \(y\) and \( (y+15)\) respectively
Adding \(9\) male students to the class increases the average weight of male students by \(1 \mathrm{~kg}\) and adding \(6\) female students increases the average weight of female students by \(0.6\)
Total male in the class \(=36+9=45\)
Total female in the class \(=24+6=30\)
\(\Rightarrow\) New average of male \(=y+16\), New average of female \(=y+0.6\)
\(\therefore\) New total average of class \(=\frac{(45({y}+16)+30({y}+0.6}{75}=\frac{(75 {y}+738)}{75} \quad-\)-(ii)
Equating (i) and (ii)
\(\frac{(75 {y}+738)}{75}={y}+9.84\)
\(y\) cannot be determined.
\(\therefore\) The data even in both the statements I and Il together are not sufficient to answer the question.