Clocks - Important Formulas; Logical Reasoning LR Notes | EduRev

Important Formulas - Clock
1. Minute Spaces

The face or dial of clock is a circle whose circumference is divided into 60 equal parts, named minute spaces.

2. Hour hand and minute hand

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

3. In 60 minutes, minute hand gains 55 minute spaces over the hour hand.
(In 60 minutes, hour hand will move 5 minute spaces while the minute hand will move 60 minute spaces. In effect the space gain of minute hand with respect to hour hand will be 60 - 5 = 55 minutes.)

4. Both the hands of a clock coincide once in every hour.
Example: 
Between 11 and 1'o clock, hands are together as shown in adjacent figure.

5. The hands of a clock are in the same straight line when they are coincident or opposite to each other.
If two hands are in opposite direction. (180° apart), then they are 30 min spaces apart. This happens once in 1 h. In a period of 12 h both hands are in opposite direction 11 times and in a day both hands are in opposite direction 22 times.

6. When the two hands of a clock are at right angles, they are 15 minute spaces apart.
This happens twice in 1 h. In a period of 12 h, the hands are at right angle 22 times (2 common positions) and in a day both hands are at right angle 44 times. 

7. When the hands of a clock are in opposite directions, they are 30 minute spaces apart.

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

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

10. If a watch or a clock indicates 9.15, when the correct time is 9, it is said to be 15 minutes too fast.

11. If a watch or a clock indicates 8.45, when the correct time is 9, it is said to be 15 minutes too slow.

12. The hands of a clock will be in straight line but opposite in direction, 22 times in a day.

13. The hands of a clock coincide 22 times in a day.

14. The hands of a clock are straight 44 times in a day.

15. The hands of a clock are at right angles 44 times in a day.

16. The two hands of a clock will be together between H and (H+1) o' clock at
(60 H/ 11) minutes past H o' clock.

17. The two hands of a clock will be in the same straight line but not together between H and (H+1) o' clock at

18. Angle between hands of a clock

• When the minute hand is behind the hour hand, the angle between the two hands at M minutes past H 'o clock
  
• When the minute hand is ahead of the hour hand, the angle between the two hands at M minutes past H 'o clock

   

  Question 2:A clock starts at noon. By 10 minutes past 5, the hour hand has turned through:

  • A.

    145°
  • B.

    150°
  • C.

    155°
  • D.

    160°

  Explanation

  Angle traced by hour hand in 12 hrs = 360°.
  Angle traced by hour hand in 5 hrs 10 min. i.e.
  

19. The two hands of the clock will be at right angles between H and (H+1) o' clock at

20. If the minute hand of a clock overtakes the hour hand at intervals of M minutes of correct time, the clock gains or loses in a day by

  

Question 3:An accurate clock shows 7 a.m. Through how many degrees will the hour hand rotate when the clock shows 1 p.m.?

• A.

  154°
• B.

  180°
• C.

  170°
• D.

  160°

Explanation

We know that angle traced by hour hand in 12 hrs. = 360°
From 7 to 1, there are 6 hours.
Angle traced by the hour hand in 6 hours = 6*(360/12) = 180°
Option B is the correct answer.

21. Between H and (H+1) o' clock, the two hands of a clock are M minutes apart at

Example 1: At what time between 4 and 5, the minute hand will be 2 minutes spaces ahead of hour hand?