The fourth proportional to $5, 8, 15$ is

Find the value of $x$ in the following proportion: $27: 72 :: x: 8$

The number that must be added to each of the numbers $8, 21, 13$ and $31$ to make the ratio of the first two numbers equal to the ratio of the last two numbers is:

The speeds of three cars are in the ratio of $1: 3: 5$. The ratio among the time taken by these cars to travel the same distance is

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?

If $A: B = 3: 4$,$B: C = 4: 5$,and $C: D = 5: 6$,then $A: D$ will be