$P$ varies inversely with the product of $Q$ and $R$. When $Q = 6$ and $R = 12$,$P = 75$. When $Q = 5$ and $R = 10$,what is the value of $P$?

The sum of three numbers is $98$. If the ratio of the first to the second is $2:3$ and that of the second to the third is $5:8$,then the second number is:

Find the mean proportional between $9$ and $64$.

If two numbers are in the ratio $2:3$ and the ratio becomes $3:4$ when $8$ is added to both the numbers,then the sum of the two numbers is

The sum of three numbers is $124$. If the ratio between the first and second is $2:3$ and that between the second and third is $7:9$,then the third number is

The incomes of $A, B$ and $C$ are in the ratio $7: 9: 12$ and their expenditures are in the ratio $8: 9: 15$. If $A$ saves one-fourth of his income,then the ratio of the savings of $A, B$ and $C$ is: