Clock angles — Between 5:00 and 5:30, at what exact time are the hands 5 minute-spaces apart (i.e., 30 degrees apart)?

Difficulty: Medium

Correct Answer: 240/11 min past 5

Explanation:


Introduction / Context:
Clock problems convert time to angles. One “minute space” on the dial is 6 degrees. “5 minutes apart” therefore means a 30-degree separation between hour and minute hands. We solve for the time t minutes after 5:00 when the angle difference equals 30 degrees.


Given Data / Assumptions:

  • Time window: between 5:00 and 5:30.
  • Minute hand speed: 6 degrees per minute.
  • Hour hand speed: 0.5 degrees per minute; at 5:00 its angle is 150 degrees.
  • Required separation: 30 degrees.


Concept / Approach:
Let t be minutes after 5:00. Minute angle = 6t. Hour angle = 150 + 0.5t. We want |6t − (150 + 0.5t)| = 30. Solve the linear equations for t and select the solution in (0, 30).


Step-by-Step Solution:

|6t − (150 + 0.5t)| = 30 ⇒ |5.5t − 150| = 30.Case giving a time in (0, 30): 150 − 5.5t = 30 ⇒ 5.5t = 120 ⇒ t = 120/5.5 = 240/11 minutes.Thus the hands are 30° apart at 240/11 minutes past 5 (≈ 21.818 minutes ≈ 5:21:49).


Verification / Alternative check:

Other solution 5.5t − 150 = 30 ⇒ t = 180/5.5 = 360/11 ≈ 32.727 minutes lies outside the 5:00–5:30 window, so it is rejected.


Why Other Options Are Wrong:

Nearby fractions (e.g., 239/11, 220/11) are close numerically but do not yield exactly 30° separation.


Common Pitfalls:

Interpreting “5 minutes apart” as a time difference rather than a 5-space (30°) angular separation.Forgetting that the hour hand also moves (0.5°/min).


Final Answer:
240/11 min past 5

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