A boy rode his bicycle Northward, then turned left and rode 1 km and again…
2023
A boy rode his bicycle Northward, then turned left and rode 1 km and again turned left and rode 2 km. He found himself 1 km west of his starting point. How far did he ride northward initially?
- A.
1 km
- B.
2 km
- C.
3 km
- D.
5 km
Attempted by 32 students.
Show answer & explanation
Correct answer: B
Solution:
Let the initial northward distance be x km.
After riding north x km the position is (0, x).
Turning left (west) and riding 1 km moves to (-1, x).
Turning left again (south) and riding 2 km moves to (-1, x - 2).
The final point is 1 km west of the start, i.e. (-1, 0). Thus set (-1, x - 2) = (-1, 0), so x - 2 = 0 and x = 2.
Answer: 2 km