RRB NTPC - Clocks and Time

11.

At what time between 7 & 8 o'clock will the hands of a watch be in the straight line but no together? 

   A.) 5 3/11 min past 7
   B.) 5 5/11 min past 7
   C.) 5 3/11 min past 7
   D.) 43min past 7

Answer: Option 'B'

When the hands of the clock are in the same straight line but not 
togerther, they are 30 minute spaces apart.
At 7 o'clock, they are 25min. spaces apart. 
Minute hand will have to gain only 5 min. 
space 55 min. spaces are gained in 60min.
5min. spaces are gained in ( 60/55 × 5) min = 5 5/11 min. 
Required time = 5 5/11 min. past 7.

12.

Between 4 & 5 O'clock, the time when the hands coincide is:

   A.) 4:21 9/11
   B.) 4:24 3/11
   C.) 4:22
   D.) 4:23 9/11

Answer: Option 'A'

4 × 30 = 120 + 0 × 2/11 
=> 240/11 = 21 9/11min 

13.

At what time between 9&10 will the hands of a watch be together? 

   A.) 45 min past 9
   B.) 49 1/11 min past 9
   C.) 48 min past 9
   D.) 47 min past 9

Answer: Option 'B'

To be together between 9 and 10 O'clock, the minute hand has to gain 45min. 
spaces 55min. spaces are gained in 60min.
45min.spaces are gained in (60/55 × 45) min. or 49 1/11 min. 
The hands are together at 49 1/11 min. past 9.

14.

At what time between 5.30 & 6 will the hands of a watch be at right angle? 

   A.) 43 7/11 min past 5
   B.) 41 2/11 min past 5
   C.) 42 min past 5
   D.) 44 1/11 min past 5

Answer: Option 'A'

At 5 o'clock, the hands are 25 min. spaces apart. 
To be at right angles and that too between 5.30 and 6, the minute hand has to 
gain 55min. spaces are gained in 60min.
4min. spaces are gained in (60/55 × 40) min. = 43 7/11min. 
Required time = 43 7/11min.past 5.

15.

At what angle the hands of a clock are inclined at 15 minutes past 5? 

   A.)  58 1/2º
   B.) 64º
   C.) 67 1/2º
   D.) 72 1/2º

Answer: Option 'A'

Angle traced by hour hand in 21/4 hrs = ( 360/12 × 21/4)º = 157 1/2º
Angle traced by min. hand in 15min. = ( 360/12 × 15 )º = 90º. 
Required angle = ( 157 1/2 )º - 90º  = 67 1/2º

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