Overlapping Clock Hands

Geometry Level 1

The time is 12:00 right now. How much time must pass until the hour hand and the minute hand overlap again?

1 hour and 6.455 minutes 1 hour and 5.455 minutes 1 hour and 5 minutes 1 hour and 6 minutes

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16 solutions

It have formula to find the angle between Hours hand and Minutes hand as Angle = 30H - (11/2)M... Here, after 1'clk, then H=1. Angle = 0. Substitute it in this formula it gives, M = 5.4555... Hence, At 13:5.455 angle should be Zero :) Simple.

6x = 30 + (x/2) ; gives - x = (60/11)

Pushpak Roy - 7 years, 1 month ago

please explain simply...:)

Shrevarna Shaji - 7 years, 1 month ago

i think it 's by logic it will give 1:5.455 what i have done first i said when the hour and minute overlap again is then they both at 1 so from 12 to 1 he the hour moving by +1 and the minute move +5 then i said as the minute hand move the hour hand moves but with a small range so it can not be just 1:05 so by logic it must be greater by this value by a small jump

Hesham Gaber - 7 years, 1 month ago

I was able to find the equation by making a ratio between minutes indicator speed and hours indicator speed as the ratio between the two-speed is 12 because when the first indicator moves 60 step , the second one moves 5 steps (step = min), so if we started from 12 am to approximately 1:05 we will find the equation as follows: (60 + x) / x = 12, where x = the number of minutes after 1 am, that is produced from the equation x = 5.4545

Sharl Philip - 7 years, 1 month ago

that s great

Humayun Khan - 7 years, 2 months ago

thats interesting

Ananya Bhattacharjee - 7 years, 2 months ago

Superb

Matheswari selvaraj - 7 years, 2 months ago

Wow

Vaishravan Mungi - 7 years, 2 months ago

asmmmm dude

sai karthik baluguri - 7 years, 2 months ago

pleas more explain how you get the formula and thank you

Yaman Rajab - 7 years, 2 months ago

how u get the formula i can't understand that formula

Izzie Stephanie - 7 years, 2 months ago

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Assuming 12 as the zero point for all measurements below we have the following equations

1.For the angle subtended by the minute hand alpha=6 degrees* minutes (one minute is basically six degrees) 2. For the angle subtended by the hour hand beta=30 degrees* hours (one hour is equal to 30 degrees on the clock face)

Mathematically a=6 M from statement I b=30 (H+M/60) from statement II

The M/60 term gives the component of the angle subtended by the hour hand within various parts of an hour

If you simplify and solve the above equations you'll get

5H=11M/12 (point of overlap)

Multiply both sides by 6 and you'll get 30H=11M/2 or 0 = 30H-11M/2 as stated by Gowtham Subramanian.

Keith de Souza - 7 years, 2 months ago

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thanq so much keith

Izzie Stephanie - 7 years, 2 months ago

Good :)

Gowtham Subramanian - 7 years, 1 month ago

Thanks for the formula

anoir trabelsi - 7 years, 2 months ago

plz xplain ur formula

zalmey khan - 7 years, 2 months ago

thanks for the formula .........

saurabh kumar agrawal - 7 years, 2 months ago

1hour5.455minutes

joel joseph - 7 years, 1 month ago

YES TRUE ......

Ayman Elyakoubi - 7 years, 1 month ago

Let hh be the number of the hour Let mm be the minutes passed the hour So the time is hh:mm

Let H be the position of the hour hand Let M be the position of the minute hand

H = hh + mm/60 M = mm/5

Now time find where the two hands meet, we need to know when H = M mm/5 = hh + mm/60 12 mm = 60 hh +mm => 11 mm = 60 hh mm = 60*hh/11 For the first meeting, hh =1 mm = 60/11 mm =5.45 minutes

Vishal Dm - 6 years, 11 months ago

i still don't get it

Peter Lin - 5 years, 3 months ago

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poo la - 5 years, 5 months ago
Liam McKnight
Apr 11, 2014

Over a twelve hour period the hands will cross over 11 times; at a little after 1.05, 2.10, etc. It is not twelve times because, in the hour starting 11.00, by the time the minute hand reaches the hour hand they are both on 12. Therefore the crossing points occur every 12/11 hours, which equals 1 hour 5 minutes and 27 3/11 seconds, or 1 hour 5.455 minutes.

Very nice fact to solve it quickly...

Nit Jon - 7 years, 1 month ago

Clock problems, hahaha.

Peter Jake Araneta - 7 years, 1 month ago
Esther Han
Apr 13, 2014

1 hour on the minute hand is 360°. 1 hour on the hour hand is 30°. 1 minute on the minute hand is 6°. 1 minute on the hour hand is 0.5°. At least one hour must pass before the minute hand and the hour hand overlap. Write an equation, with x being the amount of minutes that pass after 1 pm. The left side will be the hour hand and the right will be the minute. When they are at equal angles from 12 they will overlap. 30 + 0.5x = 6x. ; 5.5x = 30 ; x = 60/11 (answer)

Yash Singhal
Apr 4, 2014

The hands overlap at 1:5.455.so time left=13:5.455-12:00

The hour hand also moves slowly. The only time the hour hand it right above the number is when the time is O'clock like 1:00 or 2:00. So as we know that both the hands have been overlapped once at 12:00 the only closest possible time will be 1:05 when both hands are above each other. But in this case the time is 5 minutes more than the o'clock and the hour hand moves. Out of the options 1:05 cannot be possible. 1:05.445 is given and that is more accurate and the hour hand moves a little so that's the answer

Muhammad Amir - 7 years, 2 months ago

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the point is how can we do withiut options

vaishnav garg - 7 years, 2 months ago
Jeffrey H.
Nov 11, 2018

Note that after every minute, the hour and minute hand get closer together by 6 0. 5 = 5. 5 6^\circ-0.5^\circ=5.5^\circ . After one hour, the hour and minute hand are 3 0 30^\circ apart. 30 5.5 = 5.4545 \frac{30}{5.5}=5.4545\cdots , so the answer is 1 hour and 5.455 minutes.

Michael Rocheleau
Jan 27, 2016

The hands are at the same point 11 times in a 12 hour period. 12/11 = 1.090909. 1.090909 X 60 = 65.454545 minutes

Isaac Sanders
Nov 23, 2014

When the hour hands at 1, the minute hand is at 12. By the time the minute hand has reached 1, the hour hand has moved a twelth of the distance between 1 and 2. So the time is 1:05+(1/12+1/12^2+1/12^3....) which is 1:05.45454545

Sharl Philip
May 9, 2014

I was able to find the equation by making a ratio between minutes indicator speed and hours indicator speed as the ratio between the two-speed is 12 because when the first indicator moves 60 step , the second one moves 5 steps (step = min), so if we started from 12 am to approximately 1:05 we will find the equation as follows: (60 + x) / x = 12, where x = the number of minutes after 1 am, that is produced from the equation x = 5.4545

Pritam Waghode
Apr 17, 2014

ITS EASY BECAUSE AS SECOND HAND MOVES HOUR HAND ALSO MOVES

Ferriel Melarpis
Apr 13, 2014

Let x be the number of minutes needed to overlap the minute hand onto hour hand at the same angle 360deg / 60min = 6deg/min Thus, every digit(1 to 12) implies 30deg. We make our equation like this. (6x-30)/30 = x/60 /* 6deg/min times the x min we need - 30deg for we know that it is impossible to have an equal angle before 1 hour. Then divide the result to 30 to get the ratio and finally, equate it to the ratio of the x min to 60 to know if they are equal.*/ 2(6x-30) = x; 12x - 60 = x; 11x = 60; x = 60/11; x = 5.4545455 ;

Ian Mana
Apr 12, 2014

the next overlapping of the hour and minute hand is in the time of 1:00 to 2:00

if the hands of the hours and minutes overlapped then the angle from 0 minute to the hour and minute hand is the same

the angle of the hour hand is H = 3 0 o ( H ) + [ 3 0 o ( M / 60 ) ] \angle H = 30^{o} * (H) + [30^{o} * (M/60)] where M M is the number of minutes passed from 0 minute and H H is number of hours passed from 0 minute

the angle of the minute hand is M = 36 0 o ( M / 60 ) \angle M = 360^{o} * (M/60)

if we equate them and let H = 1 H=1 because it only passes 1 hour we will have a formula of 3 0 o ( 1 ) + [ 3 0 o ( M / 60 ) ] = 36 0 o ( M / 60 ) 30^{o} *(1)+ [30^{o} * (M/60)] = 360^{o} * (M/60) we will have M = 5.4545.... M = 5.4545....

So we will have 1 1 hour and 5.455 5.455 minutes before the hands overlapped again.

Dhan Raj
Apr 12, 2014

just after 1 hr (i.e at 1:0 pm) hour hand will be at 1 and minute hand at 12. After then let us consider they meet after some time 't' , after time t angle made by hour hand and minute hand from vertical will be same. Since hour hand rotate by speed 0.5 degree/min and minute hand rotates by speed 6 degree/min. After time 't' angle made by min. hand from vertical=angle made by hour hand from vertical 6 t=30+0.5 t (where 30 degree is angle between hour and minute hands at 1:00 pm ) t=30/5.5=5.4545~5.55 minute total time=1hr 5.55 minute

Lim Ken
Apr 12, 2014

Hour hand moves by 1/120 degrees per sec ( 360 / 12 x 60 x 60 ) while minute hand runs by 1/10 degrees per sec ( 360 / 60 x 60 ) 1 hour 5.455 minutes = 3926.7 seconds 5.455minutes = 327.3minutes Therefore 3926.7 x 1/120 = 32.7225 & 327.3 x 1/10 = 32.73

Indu Parkavi
Apr 12, 2014

Consider the hr hand and min hand coincide after t sec. The hour hand takes 120sec for 1 degree. So it would cover t/120 degrees in t sec. Similarly the min hand takes 10sec for 1degree. So it would cover t/10 degrees in t sec. Time taken for min hand to cover t/10 degrees= time taken for hr hand to cover t/120 degrees=t But the min hand might have completed many rounds before it coincides with hour hand Equating the angular displacements, t/10 = t/120 + 360n where n is a positive integer which denotes the number of rounds completed. Simplifying we get, t = (360 x 120 x n)/11. Converting to he's, we get, t = (12/11)n. Since the first coincidence of the min and hr hand is asked, n=1 as 1is the least value. Hence the and is 1 hr 5.455 min

Madelyn Yu
Apr 12, 2014

When the minute hand completes 1 cycle, the hour hand completes 1/12 of a cycle.
Difference in speed= 1- 1/12= 11/12
Distance to catch up= 60 scales out of 60(since the minute hand is directly over the hour hand at 12:00)
Time taken= (60/60)/ (11/12)= 1/ (11/12)= 12/11= 1 1/11 hour= 1hour 5.455 minutes


Jake Pham
Apr 12, 2014

The hour hand speed is slower than minute hand 1/12 times So it's obviously that they can't overtlap if they start same position. Let the clock run 1 hour more(1:00 - hour hand at 1 and minute hand at 12). We can easily form this (x/12+5) = x (x=5.45), left side is the distance from hour hand to overlap-place, right hand is distance of minute hand. Hence the solution is 13:5.45

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