Simplify : $$\sqrt{[(12.1)^2-(8.1)^2]÷[(0.25)^2+(0.25)(19.95)]} $$

A tap can fill the tank in 8 hours and another can empty it in 16 hours. If both the taps are opened simultaneously, the time (in hours) to fill the tank is__.

Find the value of $$ {^3\sqrt{\sqrt{.000064}}}$$.

At what simple rate of interest a sum is double in 8 years?

A field in the shape of a trapezium whose parallel sides are 200 meter and 400-meter-long, whereas each of other two sides is 260 meter long. What is the area (in m²) of the field?

The average age of five girls is 11. The oldest among them is 15 years old. What is the average age of the others?

Sanjay and Jacob start running in opposite directions from the same point at speeds of 7m/s and 5m/s. After 42 minutes, how far would they be from each other?

By reducing the circumference of a circle by 50 percent, by what percentage will its area decrease?