If $x: y = 2: 1,$ then $(x^{2} - y^{2}) : (x^{2} + y^{2})$ is

An alloy of copper and zinc is taken in the ratio $1: 2$,and another alloy of the same metals is taken in the ratio of $2: 3$. How many parts of the two alloys must be taken to obtain a new alloy consisting of copper and zinc that are in the ratio $3: 5$?

In a college,$150$ students of $MBA$ are enrolled. The ratio of boys to girls is $7:8$. There are three disciplines in the college: Marketing,$HR$,and Finance. In the Marketing discipline,there are $50\%$ girls of their total number and the boys are $40\%$ of their total number. In the $HR$ discipline,girls are $30\%$ of their total number while boys are $30\%$ of their total number. The Finance discipline has girls $20\%$ of their total number and the boys are $30\%$ of their total number. $7$ boys and $9$ girls are in $HR$ and Marketing both. $6$ boys and $7$ girls are in $HR$ and Finance both. $5$ boys and $8$ girls are in Marketing and Finance both. $2$ boys and $3$ girls are enrolled in all the three disciplines. By what percent is the number of boys in the Marketing discipline more than the number of girls in the $HR$ discipline?

The ratio of the number of boys and girls in a college is $7:8$. If the percentage increase in the number of boys and girls is $20\%$ and $10\%$ respectively,what will be the new ratio?

$A$ sum of money is to be distributed among $A, B, C$ and $D$ in the proportion of $5: 2: 4: 3$. If $C$ gets ₹ $1000$ more than $D$,what is $B$'s share (in ₹)?

₹ $1980$ is divided among $A$,$B$,and $C$ such that half of $A$'s part,one-third of $B$'s part,and one-sixth of $C$'s part are equal. What is $B$'s part (in ₹)?