Two-fifths of one-third of three-seventh of a number is $15$. What is $40$ per cent of that number?

If $\frac{3}{5}$ of a number is $23$ more than $50 \%$ of the same number,then what will be $80 \%$ of the number?

$39.897 \%$ of $4331 + 58.779 \%$ of $5003 = ?$

The weights of two iron balls are $3.5 \text{ kg}$ and $7.5 \text{ kg}$. What is the percentage weight of the first ball with respect to the second ball?

$A$ student has to secure $15\%$ marks to pass the examination. If he gets $80$ marks and fails by $70$ marks,find the maximum marks set for the examination.

In Convent Model School,$60 \%$ of the students are boys. In an aptitude test,$80 \%$ of the girls scored more than $40$ marks (out of a maximum possible $150$ marks). If $60 \%$ of the total students scored more than $40$ marks in the same test,find the fraction of the boys who scored $40$ marks or less?