RRB NTPC - Clocks and Time

16.

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 

17.

When the time in the clock is 7.20, then the angle between the hands of the clock is: 

   A.) 100º
   B.) 120º
   C.) 90º
   D.) 110º

Answer: Option 'A'

7:20 
7:4 
7~4 = 3 × 20 = 90 + 10 = 100º 

18.

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.

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