At a telephone exchange, three phones ring at intervals of 20 sec, 24 sec and 30 seconds. If they ring together at 11 : 25 a.m. When will they next ring together?

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RRB Non Technical Exam (Secunderabad) 2016 click here to view all questions

At a telephone exchange, three phones ring at intervals of 20 sec, 24 sec and 30 seconds. If they ring together at 11 : 25 a.m. When will they next ring together?

A11 : 29 a.m.

B11 : 27 a.m.

C11 : 51 a.m.

D12 : 29 p.m.

rahul ? Jan 14 '2020 at 9:33

Correct answer is: 11:27 a.m.

Explanation:

Time taken by three phones to ring together = LCM of 20, 24 and 30

⇒ Time taken by three phones to ring together = 120 seconds

(? 1 min = 60 seconds)

⇒ Time taken by three phones to ring together = $\frac{120}{60} = 2 \text{ min}$

If the three phones ring together at 11:25 am then they will next ring together after 2 minutes i.e. at 11:27 am.

∴ Time at which the phones next ring together = 11:27 am

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A clock strikes once at 1 O' clock twice at 2 O'clock thrice 3 O' clock and so, on. How many times will it strikes in 24 hours?

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RRB ASSISTANT LOCO PILOT (Allahabad) 2010 click here to view all questions

A clock strikes once at 1 O' clock twice at 2 O'clock thrice 3 O' clock and so, on. How many times will it strikes in 24 hours?

A78

B136

C156

D196

raju ? Dec 23 '2019 at 18:21

Correct answer is: 156

Explanation:

clock strikes once at 1 o'clock, twice at 2o'clock , thrice at 3 o'clock so on.
then clock strikes in 12 hour = 1 + 2 + 3 + ..... + 12 = 78
Therefore clock strikes in 24 hour = 78 X 2 = 156.

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If a watch runs 5 minutes fast every hour, then the angle traversed by a second hand in one minute is-

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RRB TC CC Exam (Bangalore) 2006 click here to view all questions

If a watch runs 5 minutes fast every hour, then the angle traversed by a second hand in one minute is-

A360

B360.5

C390

D380

Sachin Khr ? Nov 18 '2016 at 21:21

Answer is : 390
The second hand must traverse 5 * 360° = 1800° more in an hour than it should if it runs 5 minutes fast....
so,in one "normal" minute....it must traverse 1/60th of this plus its normal turn of 360°.......
$so.... [360 + \frac{1800}{60}]° = [ 360 + 30]° = [ 390]°$

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A clock strikes once at 1 O' clock, twice at 2 O' clock

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RRB TC CC Exam (Patna) 2006 click here to view all questions

A clock strikes once at 1 O' clock, twice at 2 O' clock, thrice at 3 O' clock and so on. What is the total number of striking in a day?

A156

B146

C136

D166

Akilesh Kharvi ? Nov 5 '2016 at 11:0

Answer is: 156
If it's the total number of strikes, then it's 1 + 2 +3....+ 12 all multiplied by 2, because we are calculating it for a day (24 hours).
For Calculating purpose
First 12 Hours is => 1 2 3 4 5 6 7 8 9 10 11 12
Next 12 Hours is => 12 11 10 9 8 7 6 5 4 3 2 1
-------------------------------------------------------------------------------------------------
Total 24 Hours is => 13 13 13 13 13 13 13 13 13 13 13 13 
------------------------------------------------------------------------------------------------
=>13 *12
=>156

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