Clock Problem with Strong Fundamental concepts Tricks, and Shortcuts for Competitive Exams like cds, nda ibps, ssc, railway, govt job , police,defence, ias, oas …

INTRODUCTION

     A clock is an important material in our daily life. We can not think a single day without it. We use a clock to measure the time. A clock is a device used to tell time.  A clock may be analog or digital. Parts of a Clock / Watch (analog)

◘ Crystal- a piece of glass / plastic that

  protects the face of a clock / watch

◘ Dial- the part of a clock / watch

   that is round and has hands

   that move to show you the time

◘ Face- the front of a clock,

   where the numbers are

◘ Hand- the hands on a clock

   are the long parts that move

   round and show the time.

The minute hand (MH) is also called

   the long hand (points to the minute) and

   the hour hand (HH), the short hand (points to the hour) and the                  

   thing that points to the seconds is called the second hand.

             The face of a clock or a watch is a circle which is divide d to 60 minute spaces. The minutes hand passes over 60-minute spaces while the hours hand goes over 5-minute spaces. That is, in 60 minutes the minutes hand gains 55 inutes on the hour hand.

   

    A clock is a complete circle having 360 degrees. It is divided into 12 equal parts i.e. each part is 360/12 = 30°. As the minute hand takes a complete round in one hour, it covers 360° in 60 minutes.

In 1 minute it covers 360/60 = 6°/ minute.

                      Also, as the hour hand covers just one part out of the given 12 parts in one hour. This implies it covers 30° in 60 minutes i.e. ½° per minute.

This implies,  the relative speed of the MH is 6 - ½= 5 ½ °/ minute.

              We will use the concept of relative speed and relative distance while solving problems on clocks.

In every hour

(i) The hands coincide once.

(ii) They are twice at right angles when the hands are 15 minutes  

      spaces apart.

(-1-)

(iii) They point in the opposite directions once when they are 30

       minutes spaces apart.

(iv) The hands are in the same straight line when they are

       coincident or opposite to each other.

→Too fast -If a clock indicates 9 : 20 when the correct time is                  

      9:00, it is said to be 20 min too fast.

→Too slow - If it indicates 7 : 50, when the correct time is 8 : 00,  

       it is said to be 10 min slow.

Points to Remember

● Unless otherwise mentioned all the Angles are measured  

    from North direction; In clock wise direction.

● The hands of a clock coincide 11 times in every 12 h (Since   

    between 11 and 1, the coincide only once, i.e 12 o'clock).

     →The hands coincide 22 times in a day.

● The hands of a clock point in opposite directions (in the  

    same straight line) 11 times in every 12 hours (Because  

    between 5 and 7 they point in opposite directions at 6 o'

    clock only). So, in a day, the hands point in the opposite

    directions 22 times

● In 12 hours, the hands coincide or  in opposite direction 22 times.

   In a day,the hands coincide or are in opposite  direction 44 times.

● In 12 hours, they are at right angles 22 times.(The two hands for

   right angles twice every hour. But the hands are at right angles  

   only once between 2 and 3 o’clock, & between 8 and 9 o’clock.) → In 24 hours, they are at right angles 44 times.

● Hands of the clock interchange positions after every 55  min.

Types of questions:

        Usually, three types of questions are asked from this topic:

1. Finding the time when the angle between the 2 hands is given.

2. Finding the angle between the 2 hands at a given time.

3. Questions on clocks gaining / losing time.                                                                                     

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