RAS question
A man walks 3 km towards South, turns left and walks 4 km, then turns left again and walks 3 km. How far is he from his starting point?
Correct answer: (C) 4 km.
After walking 3 km south, 4 km east and 3 km north, the man is 4 km from his starting point.
Explanation
Start at O. The man first walks 3 km south. From a south-facing position, a left turn makes him face east, so the next 4 km takes him horizontally away from the starting line. He then turns left again, now facing north, and walks 3 km. That northward movement exactly cancels the first 3 km southward movement, leaving no net north-south displacement. The only remaining displacement is the 4 km walked east. The calculation source verifies the same straight-line distance as sqrt(4^2 + 0^2) = 4, so the distance from the starting point is 4 km.
Why the other options are wrong
- (A) 5 km would apply if the final northward 3 km did not cancel the initial southward 3 km, but here the vertical displacement becomes zero.
- (B) 3 km is only the length of the southward and northward legs, which cancel each other rather than remaining as the final distance.
- (D) 7 km adds part of the route travelled, but the question asks straight-line distance from the starting point, not total walking distance.
Concept
This tests direction sense and net displacement, a recurring reasoning topic in RAS because candidates must track turns and cancel opposite movements accurately. The trap is confusing total path length with final distance from the starting point.