At what time between 2 and 3 O’clock will the hands of the clock be opposite?
2022
At what time between 2 and 3 O’clock will the hands of the clock be opposite?
- A.
2 hr. 45 min.
- B.
3 O’clock
- C.
2 hr. 43 7/11 min.
- D.
2 hr. 35 min.
Attempted by 72 students.
Show answer & explanation
Correct answer: C
Let the time be 2 : t minutes.
Angle of hour hand = 30×2 + 0.5t = 60 + 0.5t degrees.
Angle of minute hand = 6t degrees.
For the hands to be opposite, the difference between the angles must be 180°:
|6t − (60 + 0.5t)| = 180
Solve the positive case 6t − 60 − 0.5t = 180 ⇒ 5.5t − 60 = 180 ⇒ 5.5t = 240 ⇒ t = 240/5.5 = 480/11 = 43 7/11 minutes.
The negative case gives a negative t (not in the interval 0–60), so discard it.
Convert the fractional minute to seconds if desired: 7/11 minute = (7/11)×60 = 420/11 = 38 2/11 seconds (≈ 38.18 s).
Final answer: 2 hr 43 7/11 min (approximately 2:43:38.18).