The width of a rectangular hall is ½ of its length. If the area of the hall is 800 sq.m, what is the difference between its length and breadth?	Select.
A) 8 m B) 10 m C) 12 m D) 20 m E) 17 m

Rationale: "let the length of the hall be x m breadth of the hall = 1 x / 2 m area of the hall = length * breadth 800 = x * 1 x / 2 x ² = 1600 x = 40 difference between the length and breadth of the hall = x - 1 x / 2 = x / 2 = 40 / 2 = 20 m answer : d"
Answer: D