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 English Interview Questions (464) General Aptitude Interview Questions (1894) Puzzles Interview Questions (460)
Question
```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 ?```
Question Submitted By :: General-Aptitude
I also faced this Question!!     Answer Posted By

# 1
5 min-2
10-4
15-8
20-16
25-32
30-64
35-128
40-256
45-512
47.5-768

r u clear friends..

 Is This Answer Correct ? 189 Yes 11 No
Harry

# 2
47.5
 Is This Answer Correct ? 83 Yes 9 No
Sourav

# 3
47.5 mins
because 2^9=512
& 2^10=1024 but
total no. of persons=768
i.e 512+256(or 2^8)
so for 9th iteration it is 9*5=45mins
but after that only half persons(512/2=256) are to be
informed which will take 2.5mins(5/2). so
the final answer will be 45+2.5=47.5 mins....

 Is This Answer Correct ? 29 Yes 7 No

# 4
no way,wat a que?
nice ques
Ans is 47.5.Its sure.

 Is This Answer Correct ? 24 Yes 6 No
Rajez

# 5
47.5mins
 Is This Answer Correct ? 10 Yes 8 No
Guest

# 6
First in an aptitude question students are expected to keep
their eyes open to the terms used in the question. Otherwise
an aptitude paper would be the same as that of a 6th or 7th
standard question paper. The original question here was "the
same person". So the same person tells it to different
couple of people taking 5 mins each. 768 person here, so
768/2=384,384*5=1920 should have been the answer.

Now, supposing its a typical maths question, i.e. assuming
to be true, its a simple GP series which starts from 1, then
2 then 4 then 8 and so on.

So, by the problem,
2^0 + 2^1 + 2^2 +....+ 2^n = 768 (note: the first person has
been counted in the series)

so putting the summation formula for GP
1.(2^(n+1)-1) / (2-1) = 768
=> 2^(n+1) = 769
Now, 2^9 = 512 (leaving 257 behind)
Again, the count of 5 mins will be n number of times cause
the first term, i.e. 2^0 is the first person and he already
knows the secret, so the count will start essentially after
him. So n+1=9 => n=8. And for the remaining 257(actually
256, as the first person is counted in it) will be told in
extra 2.5 mins. So total, 8*5 + 2.5 = 42.5

 Is This Answer Correct ? 2 Yes 0 No
Laughing Man

# 7
@Crazyfantaxy
because it is told that the same person is telling that
secret to two new people..and then to two new people..and so
on..so the people who have been told will not be taken into
account...47.5 is therefore correct ans which Harry has given

 Is This Answer Correct ? 1 Yes 0 No
Garima

# 8
i don't understand, why are you ppl not counting the ppl who
have been told the secret before

5 min-2
10-4, total so far=6
15-8, total so far=14
20-16, tsf=30
25-32, tsf=62
30-64, tsf=126
35-128, tsf=254
40-256, tsf=510
45-512, tsf=1022
---------------
50-1024, tsf=xyz

clearly ans should lie between 40 & 45...the options
definitely do not include the correct one!

you can also solve it by using binary tree + GP + log and
find the ans to be around 43

 Is This Answer Correct ? 11 Yes 11 No
Crazyfantaxy

# 9
45 is the corrct one...many answers above r not counting the persons who hav been told earlier!!
 Is This Answer Correct ? 0 Yes 0 No
Honey Goel

# 10
khud to wrong kiya hai dusro ko bhi bakwaas sikha rahe ho

5 min-2 1 slot
10-4 2nd slot
15-8 3rd slot
20-16 4th slot
25-32 5th slot
30-64 6th slot
35-128 7th slot
40-256 8th slot

till now total people knowing secret is
1+2+4+8+16+32+64+128+256=511(approxx) heee..

for next 5 min all 256 people will be telling crap secret to
their next 2 people each.so in 5 minutes
we will have 768 people.time required will be same either
we need 257 people or 512 i.e 5minutes

so

40min + 5 min = 45 minutes.

vkx

 Is This Answer Correct ? 1 Yes 1 No
Vikas Kumar

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