a secret can be told only 2 persons in 5 mins.the same person tells to 2 more persons and so on.how long will it take to tell 768 people.
a)47.5min
b)50min
c)500min
d)49min

• 5 minute we can told to 2 person.For 2.5 minute we can talk to one person.
  
  2-4-8-16-32-->2^2-2^3-2^4 etc....
  2^9 means 512 .
  so 9*5 =45 minute
  half of the 512 is 256
  512+256 = 768
  9*5+2.5 =45+2.5=47.5 minute
• 12 years agoHelpfull: Yes(17) No(6)
• None of these
  as
  correct ans will be
  32.5 mins
  
  First person will tell secret to 2 persons in 5 mins.
  After 5 mins, 3 persons will know about the secret.
  
  Then in next 5 mins ( total 10 mins) .... 6 additional persons know the secret.
  Means total 9 persons know the secret after 10 mins.
  
  so chain will be
  1,3,9,27,81,243,729
  
  after 30 mins, 729 persons know the secret.
  In next 2.5 mins, 729 more will know the secret.
  
  so after 32.5 mins, 768 persons will know the secret.
• 12 years agoHelpfull: Yes(13) No(7)
• 1 person will tell 2 persons.
  those two will tell 4 persons.
  those 4 will tell 8 persons.
  and so on,16,32,64,128,256 and those 256 people will tell another 256 people in 2.5 min
  so,adding time and people we get 768 people in 47.5 min.
  so option a will be correct choice.
• 12 years agoHelpfull: Yes(4) No(1)
• None of these options are correct.
  Agree with Dolly.
  Around 31min take to tell 768 people..
• 12 years agoHelpfull: Yes(3) No(2)
• Dolly is definitely right.
  Time taken will be 32.5 mins
  as one person will tell secret to other in 2.5 mins.
  
  well explained by Dolly.
• 12 years agoHelpfull: Yes(3) No(4)
• 5 min-2
  10-4
  15-8
  20-16
  25-32
  30-64
  35-128
  40-256
  45-512
  47.5-768
  
  so 47.5 min is the answer
• 10 years agoHelpfull: Yes(3) No(0)
• after 2.5 minutes more 729 will know the secret that means after 32.5 minutes 1458 people will know the secret that means more than 768 person knows the secret.we cant tell how much time it will take exactly
• 12 years agoHelpfull: Yes(2) No(0)
• no dolly u dnt assume d first person d secret is being told to 2 persons simulataneously and u dnt count if dere is a actual person telling dem d secret
  
• 11 years agoHelpfull: Yes(2) No(0)
• 2+4+8+16+....=should reach 768
  therefore sum(geometric series)=2(2^n-1)(2-1)should exceed 768
  on solving, i got n=9.588 therefore chose n=10 levels.therefore total time taken=10x5=50.
• 12 years agoHelpfull: Yes(1) No(4)
• i am agree with dolly.........because the chain will 1,3,9,27,81,243,729 so after 30 minutes 729 persons will know the secret.in 2.5 minute one person will tell the secret to another one,so new 729 person will know the secret in next 2.5 minute.
• 12 years agoHelpfull: Yes(0) No(0)
• 50 min...1(5min),1+2(after 10 min),1+2+2^2(after 15 min) so 1+2+2^2+....2^n=768 where time required=(n+1)*5
  solving these two we get 2^(n+1)-1=768 or n=9(to tell the secrect requires 5 min not less than that)...so answer is 50min
• 12 years agoHelpfull: Yes(0) No(0)