At what time between 6 π‘Ž.π‘š. and 7 π‘Ž.π‘š. will the minute hand and hour hand…

2014

At what time betweenΒ 6Β π‘Ž.π‘š. andΒ 7Β π‘Ž.π‘š. will the minute hand and hour hand of a clock make an angle closest toΒ 60∘?

  1. A.

    6: 22 π‘Ž.π‘š.

  2. B.

    6: 27 π‘Ž. π‘š.

  3. C.

    6: 38 π‘Ž.π‘š.

  4. D.

    6: 45 π‘Ž.Β π‘š.

Attempted by 165 students.

Show answer & explanation

Correct answer: A

Key idea: If t is minutes after 6:00, the minute hand is at 6t degrees and the hour hand is at 180 + 0.5t degrees. The angle between them is |6t βˆ’ (180 + 0.5t)| = |5.5t βˆ’ 180|.

  • Solve |5.5t βˆ’ 180| = 60. This gives two linear equations.

  • 5.5t βˆ’ 180 = 60 β‡’ 5.5t = 240 β‡’ t = 240/5.5 = 480/11 β‰ˆ 43.636 minutes β‡’ about 6:43:38.

  • 5.5t βˆ’ 180 = βˆ’60 β‡’ 5.5t = 120 β‡’ t = 120/5.5 = 240/11 β‰ˆ 21.818 minutes β‡’ about 6:21:49.

Check which given time is closest to either exact solution by computing the angle at each provided time:

  • At 6:22 (t = 22): angle = |5.5Β·22 βˆ’ 180| = |121 βˆ’ 180| = 59Β° (1Β° away from 60Β°).

  • At 6:27 (t = 27): angle = |5.5Β·27 βˆ’ 180| = |148.5 βˆ’ 180| = 31.5Β°.

  • At 6:38 (t = 38): angle = |5.5Β·38 βˆ’ 180| = |209 βˆ’ 180| = 29Β°.

  • At 6:45 (t = 45): angle = |5.5Β·45 βˆ’ 180| = |247.5 βˆ’ 180| = 67.5Β° (7.5Β° away from 60Β°).

Conclusion: The times when the hands make exactly 60Β° between 6 and 7 are about 6:21.82 and 6:43.64. Among the given choices, 6:22 is the closest.

Answer: 6:22 a.m.

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