A rectangular lot 50 feet by 100 feet is surrounded on all sides by a concrete walk 5 feet wide. Find the number of square feet in the surface of the walk.
The average height of a class of 14 days is 5.3 feet. After new boy is admitted to the class ,the new average height now becomes 5.25. What is the height of the new boy?
A rectangle is 16 cm long and 10 cm wide. If the length is reduced by k cm and its width is increased also by k cm so as to make it a square then its area changes by