Shortly after 3 o'clock, I look at a clock. The hands of the clock, listed clockwise, are in the order: hour-minute-second.
Moreover, the angle between the hour hand and the minute hand is the same as the angle between the minute hand and the second hand.
How many seconds after 3 o'clock is it? Round off to the nearest integer . Find the smallest positive solution.
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The positions of the hands of the clock can be represented as h , m / 5 , and s / 5 , respectively, where one revolution corresponds to 12 units.
We know that m = 6 0 ( h − H ) s = 6 0 ( m − M ) where H = ⌊ h ⌋ and M = ⌊ m ⌋ are positive integers.
The problem describes the situation in which s / 5 − m / 5 = m / 5 − h ( = d > 0 ) . Substituting the expression for s , we get 1 2 ( m − M ) − m / 5 = m / 5 − h ∴ 1 1 5 3 m + h = 1 2 M ; substituting for m this becomes 1 1 5 3 ⋅ 6 0 ( h − H ) + h = 1 2 M ∴ 6 9 7 h = 1 2 M + 6 9 6 H . Thus h = 6 9 7 1 2 M + 6 9 6 H , m / 5 = 6 9 7 1 4 4 M − 1 2 H , s / 5 = 6 9 7 2 7 6 M − 7 2 0 H , and it easy to check that the angle between the hands is d = s / 5 − m / 5 = m / 5 − h = 6 9 7 1 3 2 M − 7 0 8 H .
Since it is shortly after 3 o'clock, we have H = 3 . For M we need the smallest value that makes d positive. The inequality becomes d > 0 ∴ 1 3 2 M > 7 0 8 H ∴ M > 5 1 1 4 H , in this case, M > 1 6 1 1 1 . Therefore the smallest solution after 3 o'clock is found when M = 1 7 . We calculate h = 6 9 7 1 2 ⋅ 1 7 + 6 9 6 ⋅ 3 = 3 . 2 8 8 3 8 ; subtracting 3 and multiplying by 3600 seconds per hour we find that this is 0 . 2 8 8 3 8 ⋅ 3 6 0 0 = 1 0 3 8 seconds after 3 o'clock.
It was a nice problem... Really hats off to you man
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Kind of an infuriating problem. Start with a clock at exactly 3 : 0 0 . Let m be the minutes from start, and M 1 , M 2 , M 3 be the positions of the hour, minute, and second hand respectively. Then
M 1 = 1 5 + 1 2 m
M 2 = m
M 3 = 6 0 ( m − n )
where n is the integer part of the minutes elapsed. We solve for m , n the equation, for the first instance where both sides > 0
M 2 − M 1 = M 3 − M 2
with the solution m = 1 7 . 3 0 2 7 . . . and n = 1 7 , and the number of seconds is 6 0 m = 1 0 3 8 . 1 6 . . .