the brobability of a bomb hiting a bridge is 1/2 and two direct hit are required to destroy it.the least no of bombrequired so that the probability of the bridge being destroyed is greater than 0.9 is

• @ANAMIKA
  probability of the bridge being destroyed is greater than 0.9 means
  probability of the bridge being not destroyed is lesser than 0.1
  
  now bridge is not destroyed in two cases 1 hit 0 hit
  now let n bombs are needed now find all probabilities of the bridge being not destroyed by binomial distribution i.e.
  
  [nC0+nC1]*(0.5)^n < 0.1
  
  now examine it for values n=1,2,3,4,,....
  you wil observe that for n = 1 to 6 the above inequality doesnt satisfy...it first time satisfies for n=7 ...now as least no. bombs are required said in que..so 7 will be the ans
• 11 years agoHelpfull: Yes(12) No(0)
• 7 is the correct answer
  [nC0+nC1]*(0.1)^n < 0.1
  now find when this relation is true (1st time) for n=2,3,4....
  it will be 7
• 11 years agoHelpfull: Yes(7) No(9)
• Probablility that bridge is not destroyed is 0.10
  Hence
  [nCo + nC1]*(1/2)^n
• 11 years agoHelpfull: Yes(5) No(2)
• plz explain it clearly...i cant get it
• 11 years agoHelpfull: Yes(2) No(1)
• SORRY FOR THE TYPING MISTAKE ABOVE....
  
  7 is the correct answer
  [nC0+nC1]*(0.5)^n < 0.1
  now find when this relation is true (1st time) for n=2,3,4....
  it will be 7
• 11 years agoHelpfull: Yes(1) No(0)
• Suppose n = least number of bombs that must be dropped so that the probability of destruction of the bridge is greater than 0.99. Hence the probability that the bridge is NOT destroyed is less than 0.01.
  
  If less than two bombs hit the bridge then it is not destroyed and probability of it is
  
  [ nCo + nC1 ] ( 0.5 )^n < 0.01
  
  => ( 0.5 )^n < 0.01 / (n + 1)
  
  Putting n = 1, 2, 3, and so on you find that inequality is not satisfied till n = 10 and is satisfied for n = 11.
  
  when n = 10, LHS = 0.000976 < RHS = 0.000909 is false
  when n = 11, LHS = 0.000488 < RHS = 0.000833 is true.
  
  Therefore, n = 11.
• 11 years agoHelpfull: Yes(0) No(9)
• ans. is 10...
  
  
• 11 years agoHelpfull: Yes(0) No(1)
• @ritabrata gautam- plz explain in bit detail...could nt get u..
• 11 years agoHelpfull: Yes(0) No(0)