A ladder 25m long reaches a window of building 20m above the ground. Then the distance of the foot of the ladder from the building is?
Choose the correct choice:  A) 35 m  B) 45 m  C) 30 m  D) 15 m  E) 25 m

Rationale: let it forms a right angled triangle and follow c ^ 2 = a ^ 2 + b ^ 2 then 25 ^ 2 = 20 ^ 2 + b ^ 2 b ^ 2 = 625 - 400 b = 15 answer : d
Answer: D