In the above diagram, ABCD is a rectangle with $AE = EF = FB$. What is the ratio of the areas of $\triangle CEF$ and that of the rectangle?

In the adjoining figure, $\triangle CAB$ is a right triangle, right angled at A and $AD \perp BC$. Prove that $\triangle ADB \sim \triangle CDA$. Further, if $BC = 10$ cm and $CD = 2$ cm, find the length of AD. 
In the diagram, the lines QR and ST are parallel to each other. The shortest distance between these two lines is half the shortest distance between the point P and the line QR. What is the ratio of the area of the triangle PST to the area of the trapezium SQRT?
Note: The figure shown is representative

\( AB \) is a diameter of the circle. Compare:
Quantity A: The length of \( AB \)
Quantity B: The average (arithmetic mean) of the lengths of \( AC \) and \( AD \). 
O is the center of the circle above. 