FACTS  AND  FORMULAE  FOR  CLOCKS  QUESTIONS

 

 

The face or dial of a watch is a circle whose circumference is divided into 6 equal parts, called minute spaces.

 

A clock has two hands, the smaller one is called the hour hand or short hand while the larger one is called the minute hand or long hand.

 

1. In 60 minutes, the minute hand gains 55 minutes on the hour on the hour hand.

2. In every hour, both the hands coincide once.

3. The hands are in the same straight line when they are coincident or opposite to each other.

4. When the two hands are at right angles, they are 15 minute spaces apart.

5. When the hands are in opposite directions, they are 30 minute spaces apart.

6. Angle traced by hour hand in 12 hrs = 360°

7. Angle traced by minute hand in 60 min. = 360°.

 

Too Fast And Too Slow : If a watch or clock indicated 8.15, when the correct time is 8, it is said to be 15 minutes too fast.

 

On the other hand, if it indicates 7.45, when the correct time is 8, it is said to be 15 minutes too slow.

Q:

The reflex angle between the hands of a clock at 10.25 is

A) 197 1/2 B) 167 1/2
C) 157 1/2 D) 187 1/2
 
Answer & Explanation Answer: A) 197 1/2

Explanation:

Angle traced by hour hand in 125/12 hrs = (360/12 * 125/12) = 312102

 

 

 

Angle traced by minute hand in 25 min = (360/60 * 25) = 1500

 

 

 

 Reflex angle = 3600-31212-1500=3600-162102=197102

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Q:

How much does a watch lose per day, if its hands coincide ever 64 minutes?

A) 32 8/11 B) 33 8/11
C) 34 8/11 D) 35 8/11
 
Answer & Explanation Answer: A) 32 8/11

Explanation:

55min spaces are covered in 60min

60 min. spaces are covered in (60/55 x 60) min= 65+5/11 min.

loss in 64min=(65+5/11)- 64 =16/11

Loss in 24 hrs (16/11 x 1/64 x 24 x 60) min= 32 8/11.

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Q:

A watch which gains 5 seconds in 3 minutes was set right at 7 a.m. In the afternoon of the same day, when the watch indicated quarter past 4 o'clock, the true time is:

A) 4pm B) 5pm
C) 6pm D) 7pm
 
Answer & Explanation Answer: A) 4pm

Explanation:

Time from 7 am to 4.15 pm  = 9 hrs 15 min = 374 hrs 

 

3 min. 5 sec. of this clock = 3 min. of the correct clock. 

 

Now 3min.5sec. is37720 hrs of this clock = 3 min.is120 hrs of the correct clock 

 

374 hrs of clock = 120×72037×374 hrs of the correct clock. 

 

  = 9 hrs of the correct clock. 

 

 The correct time is 9 hrs after 7 am. i.e., 4 pm.

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Q:

A watch gains 5 seconds in 3 minutes and was set right at 8 AM. What time will it show at 10 PM on the same day ?

A) 10 : 27 : 41 AM B) 8 : 51 : 04 AM
C) 9 : 45 : 15 PM D) 10 : 23 : 20 PM
 
Answer & Explanation Answer: D) 10 : 23 : 20 PM

Explanation:

The watch gains 5 seconds in 3 minutes = 100 seconds in 1 hour.

From 8 AM to 10 PM on the same day, time passed is 14 hours.

In 14 hours, the watch would have gained 1400 seconds or 23 minutes 20 seconds.

So, when the correct time is 10 PM, the watch would show 10 : 23 : 20 PM

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Q:

At what time between 3 and 4 o’clock will the minute hand and the hour hand are on the same straight line but facing opposite directions ?

A) 3:15 2/8 B) 3:49
C) 3:49 1/11 D) 3:51
 
Answer & Explanation Answer: C) 3:49 1/11

Explanation:

On straight line means 180 degree angle.
180 = 11/2 min – 30 hrs
180 = 11/2 m – 30 × 3
180 = 11/2 m – 90
(180 + 90) 2 = 11 m
m = 540/11 = 49 1/11 minutes.

 

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Q:

In 16 minutes, the minute hand gains over the hour hand by -

A) 16 deg B) 80 deg
C) 88 deg D) 94 deg
 
Answer & Explanation Answer: C) 88 deg

Explanation:

In one hour, the minute hand gains 330° over the hour hand. i.e., 60 minute, the minute hand gains 330° over the hour hand.

∴ In 16 minutes, the minute hand gain over the hour hand by fraction numerator 330 degree over denominator 60 end fraction cross times 16 degree equals 88 degree

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Q:

At what time, between 3 o’clock and 4 o’clock, both the hour hand and minute hand coincide each other  ? 

A) 3:16 7/11 B) 3:16 11/4
C) 3:30 D) 3:16 4/11
 
Answer & Explanation Answer: D) 3:16 4/11

Explanation:

Coincide means 00  angle.

This can be calculated using the formulafor time A to B means  [11m/2 - 30 (A)]

Here m gives minutes after A the both hands coincides.

Here A = 3, B = 4

0 =11m/2 –30 × 3
11m = 90 × 2 = 180
m= 180/11 = 16 4/11

So time = 3 : 16 4/11

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Q:

An accurate clock shows 7 o'clock in the morning. Through how may degrees will the hour hand rotate when the clock shows 3 o'clock in the afternoon?

A) 144º B) 168º
C) 180º D) 150º
 
Answer & Explanation Answer: C) 180º

Explanation:

Angle traced by the hour hand in 6 hours =360o12×6 = 180o.

 


 

 


 
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