A secret can be told only 2 persons in 5 minutes .the same person tells to 2 more persons and so on . How long will take to tell it to 768 persons ?

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ranjan

  • Mar 28th, 2006
 

1   person called in 5/2 min=2.5 min

   then 768 person2.5*768=1920 min

      32 hours

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saraswathy

  • Jun 7th, 2006
 

i read somewhere that the answer for this question is 47.5 minutes.any idea how that answer came?

jegadeesan

  • Jul 13th, 2006
 

 A secret can be told only 2 persons in 5 minutes .the same person tells to 2 more persons and so on . How long will take to tell it to 768 persons ?

                 plz briefly explain that question.

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abi

  • Jul 25th, 2006
 

2 persons hear the answer in 5 min. each one tels the secret to other 2... like wise it continues upto log(768) to base 2 then we get 9.5this multipled by 5 gives the ans47.5 min 2 2< 22< 2 2< 25 5 5like wise.....

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lalit

  • Aug 4th, 2006
 

yeah it is around 47 minutes

this is due to as 1 person tells in 5 minute the thing to 2 persons now these 2 persons can tell this stuff to more persons and so on

ie 2 4 8 16 32 64 and so on...

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rasesh ajwalia

  • Nov 20th, 2007
 

one person telling to 2 that means he takes 2.5 min to 1 person....


now, 1 is telling to another 2 this two telling another 2 person and so on....

that means chain is 1 to 2, 2to 4, 4to 8, 8 to 16...

means 2 48 16....512.
upto this this will take 45 min now these person means 256 telling only 1 the total person willbe 768 & 45 + 2.5 = 47.5 min...

  
      2 persons are told abt the secret in 5min...

     same way these 2 inform to 4 n then
      these 4 informs to 8......

       -> 2 -> 4 -> 8 -> 16 -> 32 -> 64 -> 128 -> 256 -> 512 

         By now 9* 5 min got over = 45 min (5 min  for each arrow ->)

    But still 256 ppls are left to be informed...
          since 512+256 = 768

-> 2 -> 4 -> 8 -> 16 -> 32 -> 64 -> 128 -> 256 -> 512 -> (512+256) = 768

     If these 512 ppl will inform 1024 ppl (512 * 2) in 5 min
                  512 ppl will inform 512 ppl (512 *1)    in 2.5 min   
                  512 ppl will inform 768 ppl (512 * 1.5=768) in (2.5 * 1.5) min
                                                                                       =3.75

 So, Total time taken =  45 + 3.75 min
                                  =  48.75 min

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anand3186

  • Jul 20th, 2009
 

In the firs 5 mins, 2 persons will get to know it.

2nd 5 mins 2+4.

3rd 5 mins, 2+4+8.

so the patern gos like this...

2 (5 mins)
6 (5 mins)
14 (5 mins)
30 (5 mins)
62 (5 mins)
126 (5 mins)
254 (5 mins)

till here total = 494.

rem persons  = 768 - 494 = 274.


I the next patern, 510 people will get to know in 5 mis.

so, 274 personswill know the answer in  (274*5/510) = 3mins 26sec (apprx)

so, total time  = 7*5mins + 3ins 26secs. = 38mins 26sec.

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Ans:35 minuites.

1 person told to 2 people in 5 minuites
3 -6-10
9-18-15
27-54-20
81-162-25
243-486-30
       upto now 243+486=729 people knows the information
  768-729=39 people will know the information in another 5 minuites.
    so,the answer is 35 minuites.

shruthidn

  • Mar 19th, 2010
 

2^9=512
so it takes 45 min to tell secrets to 512 members.
now 2^10=1024
takes 50min to tel secrets to 1024 members.
The answer should be between 50 & 45.
It takes another 2.5min to tel secret to 256 members.
In total 512+256=768 i.e 47.5min.

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varuns8788

  • Jan 11th, 2011
 

This can be solved simply if we consider it a tree.
that is....2 tells 2 (in 5 mins)
2 tells 2 (in 5 mins)
2 tells 2 (in 5 mins)
2 tells 2 (in 5 mins)
and so on...
by
the formula we can take 2^n=768
we get (2^8)*3=768
that means it takes time to say to 9th level plus an
extra guy..
we get 45mins till 9th level (5mins*9)and 2.5mins for a single guy (since 5min is for 2 guys)
therefore it takes a total of 45+2.5=47.5mins

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venkateshwar

  • May 5th, 2012
 

The answer is like this
1st - 768/2
2nd - 384/2
3rd - 192/2
4th - 96/2
5th - 48/2
6th - 24/2
7th - 12/2
8th - 6/2
9th - 3/2
10th- 1/2 = 0.5

i.e., 9.5 iterations
then 9.5 * 5 = 47.5 Hence proved :)

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venkateshwar

  • May 5th, 2012
 

We should divide the given number i.e., 768 by 2 till it gets less than 1
(because everybody should be told the secret)
for this it will take 9.5 Iterations
so, 9.5 * 5 = 47.5
Hence proved :)
It is the correct answer.. even checked

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ruchi

  • May 27th, 2013
 

1920 mint

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divyanshu

  • Sep 2nd, 2014
 

one person telling to 2 that means he takes 2.5 min to 1 person....


now, 1 is telling to another 2 this two telling another 2 person and so on....

that means chain is 1 to 2, 2 to 4, 4 to 8, 8 to 16...

means 2 4 8 16....512.
up to this this will take 45 min now these person means 256 telling only 1 the total person will be 768 & 45 + 2.5 = 47.5 min...

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Abhishek

  • Jan 28th, 2015
 

I dont know what you guys are smoking, you are not adding people who are being told the secret.

Here is the correct answer. Reply me if I am wrong.

5 mints=>2 secret known by=2ppl
10 mints=>2to4 (2+4) =6ppl
15 mints=>6to12 (6+12) =18ppl
20mints=>18to36 (18+36) =54ppl
25 mints=>54to108 (54+108) =162ppl
30 mints=>162to324 (162+324) =486ppl
35mints=>486to 972 (486+972) = 1458 ppl
so ans is 35mins

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