In a school 80% of the students are girls. The number of boys are 500. Then the total number of students in the school is

If $$ {x+{1\over x}}=3$$ then find the value of $$ {x^2}-{1\over {x^2}}$$:

A person rows a distance of $$ {3{3\over4}{ \ km}}$$ upstream in $$ {1{1\over 2}{\ hours}}$$ and a distance of 13 km downstream in 2 hours. How much time ( in hours) will the person take to row a distance of 90 km in still water?

The simple and compound interest that can be earned in two years at the same rate is Rs 1500 and Rs 1575 respectively. What is the rate (% per annum) of interest?

Direction: What is the approximate value will come in place of the question mark(?) in the following questions?
5682 ÷ 63 × 36=? ×19

Two 6 cm diameter balls dipped in a 6 cm radius cylindrical vessel of water. Find the height of water in the vessel?

The angle of elevation of the top of a tower from two points A and B lying on the horizontal through the foot of the tower are 159 and 30° respectively. If A and B are on the same side of the tower and AB = 48 meter, then the height of the tower is; 

In the given figure, the ratio of the area of the largest square to that of the smallest square is: