Two alloys contain zinc and copper in the ratio of $2:1$ and $4:1$. In what ratio should the two alloys be mixed to get a new alloy having zinc and copper in the ratio of $3:1$?

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?

What number should be added to or subtracted from each term of the ratio $17: 24,$ so that it becomes equal to $1: 2?$

In a mixture of petrol and kerosene,the quantity of petrol is $99 \text{ litres}$. If this same quantity of petrol were present in another mixture of petrol and kerosene where the total volume is $198 \text{ litres}$ less than the actual mixture,the concentration of petrol in the actual mixture would be $13.33 \%$ less than that of the new mixture. What is the concentration (in $\%$) of petrol in the actual mixture?

The fourth proportional to $0.2, 0.12$ and $0.3$ is

The ratio of the speeds of Aman,Kamal,and Manan is $4: 5: 6$ respectively. What is the ratio of time taken by Aman,Kamal,and Manan respectively to cover the same distance?