Latest CTS Aptitude Question SOLUTION: 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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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 ?

Solution

at start one person will tell to 2 persons, it will take 5 min, now that 1+2 = 3 persons will tell this to next 6 persons, then 1+2+6 = 9 persons will tell to next 18 persons, then 1+2+6+18 = 27 persons to 54 similarly 1+2+6+18+54 = 81 persons will tell this to 162 persons similarly 1+2+6+18+54+162 = 243 persons will tell this to 486 persons, upto this step total persons who have listened this secret = 2+6+18+54+162+486 = 728, and total time taken upto this step = 5*6 = 30 min, now next 5 min will be sufficient to tell this message to next 40 persons so total time taken = 35 min

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Asked In CTS Kumar (12 years ago)

Solved Read Solution (8)

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Read Solution (8) :

saiharsha  (10 years ago)

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

Is this solution Helpfull? Yes (27) | No (5)  

Vincent koijam  (12 years ago)

40 minutes
proof:
in first 5 min 1 person tells to 2 other people , in the next 5 min 2+1 tell to 6 other people , in the next 5 min 6+2+1 tell to 18 new people n in the next 5 min 18+6+2+1 tell to 27*2 new people n so on

Is this solution Helpfull? Yes (6) | No (9)  

Rahul Singh Kanwal  (10 years ago)

2^x = 768

x = log(768) / log(2)

x = 9.5849

Then times that by the doubling time = 5 minutes

9.5849 * 5 = 47.9245 minutes = 47 minutes, 55.47 seconds

Is this solution Helpfull? Yes (6) | No (1)  

Karthick Babu  (12 years ago)

Ans is 50 min.
1->2->4->8->16......->512->1024
2^9=512 After this definitely one person need 5 min to tell to others. So totally 10 * 5 min =50 min

Is this solution Helpfull? Yes (5) | No (10)  

  (5 years ago)

2^8 x 3 = 768
to tell the secret to 2^1 persons it takes 5(5 x 1) minutes
to tell the secret to 2^8 persons it takes 40(5 x 8) minutes
then there will be remaining 3 persons who can be split as (2 + 1) persons
so obviously the time for (2 + 1) persons will be (5 + 2.5) minutes which will be 7.5 minutes
so total 2^8 x 3 (768) persons it will take (40 + 7.5)= 47.5 minutes

Is this solution Helpfull? Yes (2) | No   

pavan  (12 years ago)

768*5/2 = 1920

Is this solution Helpfull? Yes (1) | No (13)  

sethupathi.s  (8 years ago)

The ans is exactly 45min. person
5-> 1+2=3
5->3*2=6
5->6*2=12
5->12*2=24
5->24*2=48
5->48*2=96
5->96*2=192
5->192*2=384
5->384*2=768, so this is the correct answer thing logically. exactly at the 45th minutes the truth will pass to 768 persons

Is this solution Helpfull? Yes (1) | No   

dharmil  (12 years ago)

384*5 minutes=1920 minutes

Is this solution Helpfull? Yes | No (14)  

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