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.

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.....

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...

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...

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

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.

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.

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

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

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

ruchi

May 27th, 2013

1920 mint

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...

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

## 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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