The students in three classes are in the ratio $2:3:5$. If $20$ students are increased in each class,the ratio changes to $4:5:7$. The total number of students before the increase was:

When $30$ percent of one number is subtracted from another number,the second number reduces to its four-fifth. What is the ratio between the first and the second number respectively?

Four years ago,the father's age was three times the age of his son. The total of the ages of the father and the son after four years will be $64$ years. What is the father's age at present (in years)?

There is a ratio of $5:4$ between two numbers. If $40\%$ of the first number is $12$,then $50\%$ of the second number is:

$A$ and $B$ are two alloys of gold and copper prepared by mixing metals in the ratio $7:2$ and $7:11$ respectively. If equal quantities of the alloys are melted to form a third alloy $C$,the ratio of gold and copper in $C$ will be

The ratio of ages between $A$ and $B$ is $6: 5$ and the age of each $C$ and $D$ is $\frac{9}{10}$ times that of $B$. The age of $F$ is less than $A$ but greater than $B$. The ratio of ages between $B$ and $E$ is $2: 3$. Also,the age of $A$ is $3 \text{ years}$ less than $E$. What is the ratio of the ages of $A$ and $F$ if all the ages are integers?