Find the sub-duplicate ratio of $81: 64$.

Find the $4^{th}$ proportional to $4, 16$ and $7$.

If $A: B = \frac{1}{2}: \frac{3}{8}$,$B: C = \frac{1}{3}: \frac{5}{9}$ and $C: D = \frac{5}{6}: \frac{3}{4}$,then the ratio $A: B: C: D$ is

The ratio of the sum of two numbers and their difference is $5:1$. The ratio of the greater number to the smaller number is

The salaries of $A, B, C$ are in the ratio $2: 3: 5$. If increments of $15\%, 10\%,$ and $20\%$ are allowed respectively in their salaries,then what will be the new ratio of their salaries?

The flight fare between two cities is increased in the ratio $9:11$. What is the increase (in ₹) in the fare,if the original fare was ₹ $18,000$?