Let be the centre of a standard clock face and let be the point at the 12 o'clock position. Let be the end point of the hour-hand and the end point of the minute-hand. At some time between 10:00 o'clock and 11:00 o'clock, accurate to the nearest second, and this can be represented as hours, minutes, seconds.
Find the smallest possible value of .
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Let the angular speeds of hour-hand and minute-hand by ω h and ω m respectively, then we have ω h = 6 0 3 0 ∘ = 2 1 ∘ /min and ω m = 6 0 3 6 0 ∘ = 6 ∘ /min .
At 10:00 o'clock, ∠ A O T = 6 0 ∘ and ∠ B O T = 0 ∘ . Let the required ∠ B O T − ∠ A O T be θ and the time after 10:00 to reach the required angles be t minutes, then for minute-hand: θ = ω m t = 0 . 5 t and hour-hand: θ = 6 0 − ω h t = 6 0 − 6 t , then:
2 t t 1 3 t ⟹ t = 6 0 − 6 t = 1 2 0 − 1 2 t = 1 2 0 = 1 3 1 2 0 min ≈ 9 min 1 4 s
The time is therefore 1 0 : 9 : 1 4 , ⟹ X + Y + Z = 1 0 + 9 + 1 4 = 3 3