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Dr. Keh-Gong Shih


Figure 701 : Clock - Angle between two hands


  • Q01 | - Diagram : Clock - Angle between two hands
  • Q02 | - Angle of short hand
  • Q03 | - Angle of minute hand
  • Q04 | - Time when hour hand and minute hand have 180 degrees angle
  • Q05 | - Angle of hour hand when two hands make 180 degree angle


Q01. Diagram : Angle between two hands


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Q02. Angle of hour hand

Definition
  • Each hour = 360 degrees/12
  • Angle of hour hand relative to 12 o'clock
    • 1 o'clock = 30 degrees
    • 2 o'clock = 60 degrees
    • 3 o'clock = 90 degrees
    • 4 o'clock = 120 degrees
    • 5 o'clock = 150 degrees
    • 6 o'clock = 180 degrees

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Q03. Angle of minute hand

Definition
  • Each minute = 360 degrees/60 = 6 degrees
  • Angle of minute hand relative to 12 o'clock position
    • At 1 minute = 6 degrees
    • At 15 minute = 90 degrees
    • At 30 minute = 180 degrees
    • At 45 minute = 270 degrees

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Q04. Angle between two hands

Time when two hands two hands make 180 between 3 and 4 o'clock
  • Let hour = x
  • Let minute = y
  • The time is x + y/60
  • Hence angle of short hand = (x + y/60)*30
  • Hence angle of minute hand = 6*y
  • Since two hands are coincided
  • Hence (x + y/60)*30 = 6*y - 180
  • Hence y = (30*x + 180)/(6 - 0.5)
  • Between 3 and 4 o'clock, x = 3
  • Hence y = (90 + 180)/5.5 = 49.09 minutes
  • Hence the time is 3 o'clock 49.09 minutes

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Q05. Angle of hour hand when hour hand and minute hand coincide

Angle of short hand when two hands coincide between 3 and 4 o'clock
  • Let hour = x
  • Let minute = y
  • The time is x + y/60
  • Hence angle of short hand = (x + y/60)*30
  • Hence angle of minute hand = 6*y
  • Since two hands are coincided
  • Hence (x + y/60)*30 = 6*y
  • Hence (x + y/60)*30 = 6*y - 180
  • Hence y = (30*x + 180)/(6 - 0.5)
  • Between 3 and 4 o'clock, x = 3
  • Hence y = (90 + 180)/5.5 = 49.09 minutes
  • Hence the time is 3 o'clock 49.09 minutes
verify
  • Short hand at (3 + 49.09/60)*30 = 114.54 degrees
  • Long hand at 49.09*6 = 294.54
  • Angle between two hands = 294.54 - 114.54 = 180 degrees

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