What should come in place of the question mark (?) in the following mathematical statement?
$${{?^6÷16=108}}$$

Directions : In an Institution there are 800 students. Students use different modes of transport for going to the institution and return. The given pie diagram represents the requisite data. Study the diagram carefully and answer the questions.

The number of students who go to institute on foot is 

The average of 10 observations is 21. A new observation is included and the average of these 11 numbers is 1 less than the prevoius average. The 11^th observation is____

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

Directions: The table given here shows the production of five types of cars by a company in the year 1989 to 1994. Study the table and answer questions.

In which year the total production of cars of types P and Q together was equal to the total production of cars of types R and S together?

The acid and water in two vessels A and B are in the ratio 4:3 and 2:3. In what ratio should the liquid in both the vessels be mixed to obtain a new mixture in vessel C containing half acid and half water?

If the total surface area of a sphere of radius r cm is equal to the total surface area of a cube of side s cm, which of the following is true?

$$\left({1\over cosecθ}-{1\over sinθ} \right)+{1\over {cosecθ-cotθ}} -{1\over secθ+tanθ} =?$$