Tick Tock Angle

Geometry Level 2

What is the measure, in degrees, of the smaller angle formed by the hour hand and the minute hand of a clock at 12:20?

100 120 110 130

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10 solutions

Discussions for this problem are now closed

Tom Li
Mar 29, 2014

The clock is 360 degrees (it's a circle), 360 / 12 (hours) = 30 degrees for each hour.

The short hand clock does not stop at 12 when its 12:20. 12:(20) is 1/3 of a clock which is 1/3 of a circle or 1/3 of 360 degree.

Thus 12:20 short hour hand is at 1/3 way to 1:00 .

12 to 12:20 is 30 degrees x 4 = 120 - (1/3 x 30) = 120 - 10 = 110

The clock is at 110 degrees when it's 12:20

the irony is... some math teachers will answer 120 instead of 110...

Korry Naemon - 7 years, 2 months ago

they geometry rate is -1

math man - 7 years ago

Thanks Tom Li for giving such a clear explanation

Ali Hassan - 7 years, 1 month ago

No problem :D

Tom Li - 7 years, 1 month ago

Your solution is good but try mine, its simpler than yours (think so )

Ashley Shamidha - 7 years, 1 month ago

This was a common type of question that we used to ask our Year 7s. It's a good question that leads to harder questions.

Sam Cheung - 7 years ago
Arpit Sah
Apr 2, 2014

Angle covered by MINUTE hand in 20 Minutes = 360 60 × 20 \frac{360}{60}\times20 = 12 0 120^{\circ}

Angle covered by HOUR hand in 1hour = 360 12 × 1 \frac {360}{12}\times1 = 3 0 30^{\circ}

Angle covered by HOUR hand in 20 Minutes = 30 60 × 20 \frac{30}{60}\times20 = 1 0 10^{\circ}

Therefore, smaller angle formed by the hour hand and the minute hand of a clock at 12:20 = 12 0 120^{\circ} - 1 0 10^{\circ} = 11 0 110^{\circ}

heyhhey! Read your second line. (360/60)*1=30??? It should be 12 instead of 60 which means 360 degrees in 12 hours.

Aji Karunakaran - 7 years, 2 months ago

Sorry, it should be (360/12)*1 = 30 .

Arpit Sah - 7 years, 2 months ago

thanks for the best explanation

zalmey khan - 7 years, 2 months ago

Your solution is good but try mine, its simpler than yours (think so )

Ashley Shamidha - 7 years, 1 month ago
Dana Chiueh
Apr 10, 2014

I actually did it somewhat differently.....

If the hour hand did not move and stayed at the "12" position even at 12:20, the minute hand would (still) be at the "4" position and thus the angle would be 4 spaces, or 4/12, or 120 degrees.

However, since the hour hand does move, we know that the angle must be less than 120; thus, we can rule out the choices "120" and "130".

Since the hour hand moves 1/12 of the clock per hour, and 20 minutes (the 20 part of 12:20) is 20/60 of an hour, or 1/3, we do 1 3 × 1 12 = 1 36 = 10 360 = 10 \frac{1}{3} \times \frac{1}{12} = \frac{1}{36} = \frac{10}{360} = 10 degrees.

Since the answer must be less than 120, it must be 120 10 = 110 120 - 10 = \boxed{110}

Diyanko Bhowmik
Apr 2, 2014

First calculate the angle between the minute hand and 12 'o' clock which comes to 120 degrees. Then, the angle made by the hour hand with 12 'o'clock comes to = (20/60x12) x 360 = 10 degrees. So the angle will be = 120-10 = 110 degrees

Caio Mathias
Apr 27, 2014

Para encontrar o ângulo entre os ponteiros do relógio podemos usar a seguinte fórmula: | 11m - 60h | /2 , onde m são os minutos e h são as horas. Substituindo os valores na fórmula temos: | 11.20 - 60.12| /2 = 250. Como queremos saber o menor ângulo bastar subtrair 250 de 360, que é igual a 110

Mauricio Jadulos
May 4, 2014

Just by analyzing the clock, from 12 to 4 the angle between the hour hand and minute is equal to 120 degrees ( since the circle is divided equally into 12 spaces and the angle between spaces is 30 degrees.) At 12:20 the hour hand theoritically will travel (20/60)x30 = 10 degrees.. therefore from the figure the angle required is 120 - 10 = 110 degrees..

Sunil Pradhan
Apr 13, 2014

The formula for angle between two hands of a clock = ø = 30h – 11/2 m when minute hand is behind the hour hand or ø = 11/2 m – 30 h when it is ahead of hour hand. where h is hours completed and m is minutes completed.

at 12 O'clock h = 0 and m = 20 so a 12:20 ø = 11/2 m – 30h = 11/2 × 20 – 0 = 110°

Bhairesh Murthi
Apr 24, 2014

for (12+20/60)hr angle traced by hour hand is (360/12)*(12+20/60)=370 degrees

Angle traced by mint hand in 20 min is (360/60)*20=120 degrees.

==>angle difference between them is 370-120=250 degrees.

but the min angle between them is 360-250=110 degrees

The hour hand goes exactly 1/12 times slower than the minute hand (that's why hour hand moves just a round while minute hand completes 12 round). a full round= 360 degree i.e. a minute step= 360/60=6 deg

  the  minute hand is at 20 min.
 from 12 o clock it has moved 6*20=120 deg.
  Meanwhile, the hour hand has moved from 12 o clock 120/12=10 deg.
   i.e. the angle between them= 120-10 deg=110 deg
Sarath Ceh
Apr 2, 2014

for every 10min there wil be a increase in 5 degree in hour hand. similarly wen 12.20. 12- 20 wil be 120 degree but the hour hand moves 10 degree so the value wil be 110 degree....

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