Clock Problems

Theory:

We all know, a clock is a device that measures and shows time. It has two arms. The longer arm is minute hand and the shorter arm is hour hand. Some clocks also have a thin short arm known as the second hand.

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The dial of the clock is a circle.( Yes.. yes.. it means the total number of degrees on a clock is 360°.) The circumference of the dial is divided into 12 parts, called hour spaces. Each hour space is divided into 5 parts called as minute spaces. Thus the whole circumference of dial is divided into 12 × 5 = 60 minute spaces.

I know, now you might be wondering about the angle covered by the hour hand and minute hand for various time intervals. Here is the table giving its details.

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Some facts about clocks: 

  • Did you know? During every hour, minute hand and hour hand coincides once. i.e the angle between these two hands is 0°.
  • Thus, in 24 hours, the two hands coincided with each other 24 times!!
  • Both hands coincide after every 720/11 mins. That means, approximately, after every 65 minutes, the two hands coincide!!!

Some important types of clock problems:

Type 1) What is the angle between the minute hand and hour hand of a clock at any given time?

Type 2) What is the time when the angle between minute hand and hour hand is given?

Type 3) What is the time gap between two instants when angle between minute hand and hour hand is given?

Formula to find angle between the hour hand and minute hand:

Angle between H hrs and M mins = |60H – 11M| / 2

where H is the hour reading and M is the minute reading for the given time.

To find mirror image of given time:

Type 1) Time between 11 and 1: Substract the given value from 23:60

Type 2) Any time (except the time between 11 and 1): Substract the given value from 11:60

Watch out this space for more practice problems and CSIR NET exam solutions on clock problems.

 

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Logical Puzzles

Theory:

These type of questions asked in CSIR NET Paper-I are the simplest amongst all the questions asked by them.

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Attempt these questions like a detective!!  🙂 Just like Vyomkesh Chandra Bakshi, solve the puzzle by deducing from the observations and visualising scenario in real world.

With the following steps one can be fairly capable of solving logical puzzles asked in these exams.

Step 1: Note all observations from the given question. ( Phew!!)

Step 2: Analyse every noted observation by comparing it with the remaining observations. ( Where do I see a contradiction?? Wooohooo.. Here I see it!!)

Step 3: Eliminate impossible / incorrect observations. (GET OUT.. miss. Misleading option!!)

Step 4: Cross check whether the remaining observation(s) is/(are) suitable. (Finally.. Are you the one I am looking for??? Ummmhmmm… )

Step 5: If correct observation is found, then stop the process .(Hurrraaahhh.. I found  it!! I found it!!.) Else, go back to step 2.(Oh no!!! Where did I go wrong??)

Solved examples from recent CSIR UGC NET Paper-I

1)  CSIR NET DEC 2014

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Solution: d

Clue 1:

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Clue 2:

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Clue 3:

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Sorry for the inconvinience caused by my pathetic scribbling.


2) CSIR NET DEC 2014

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Soln: c

Clue 1: Total number of days is the total number of lunch taken.

Clue 2: Use statements (2) and (4) to find out total non-veg lunch meals.

Clue 3: Use statement (3) to find total veg lunch meals.


3) CSIR NET JUNE 2014

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Soln: b

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4) CSIR NET DEC 2013

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Soln:c


5) CSIR NET JUNE 2015

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Soln : c


6) CSIR NET DEC 2012

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Soln: a

Gif source: Giphy.com

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