What is h equal to ?

Consider the following for the next two (02) items that follow :<br>A hall is of length l, breadth b and height h. The maximum distance between any two points (say P and Q) inside the hall is 14 m, whereas the maximum distance between two points (say P and R) on the floor is 6\sqrt{5} m.

  1. A. 3.5 m
  2. B. 4 m
  3. C. 4.5 m
  4. D. 5 m

Correct Answer: B. 4 m

Explanation

The maximum distance inside the hall is the body diagonal \sqrt{l^2+b^2+h^2} = 14. The maximum distance on the floor is the face diagonal \sqrt{l^2+b^2} = 6\sqrt{5}. Squaring both gives l^2+b^2+h^2=196 and l^2+b^2=180. Subtracting them yields h^2 = 16, so h = 4 m.

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