Question

A research team conducted a study showing that approximately 30% of all businessmen who wear ties wear them so tightly that they actually reduce blood flow to the brain, diminishing cerebral functions. At a board meeting of 30 businessmen, all of whom wear ties, what are the following probabilities?
a. at least one tie is too tight
b. more than two ties are too tight
c. no tie is too tight
d. at least 18 ties are not too tight

Answer 1

Answer:

a) 0.9998

b) 0.9979

c) 0.7

d) 0.9155

Step-by-step explanation:

P( people who wear their ties tightly ) = 0.3

P( people who do not wear their ties tightly ) = 1 - 0.3 = 0.7

sample size ( n ) = 30

Given that the events are independent and there are only two outcomes we will apply Binomial distribution

a) P( at least one tie is too tight )

P ( x ≥ 1 ) = 1 - P ( x < 1 ) = 1 - P ( x = 0 )

       = 1 - 0.00002 = 0.9998 ( excel function: 1 - BINOMDIST(0,30,0.3,0) )

b) P( more than two ties are too tight )

P ( x > 2 ) = 1 - P ( x ≤ 2 ) = 1 - BINOMDIST(2, 30, 0.3, 1 )

                                       = 1 - 0.002113178

                                       = 0.9979

c) P ( no tie is tight )

P ( x = 0 ) = 0.7

d) P( at least 18 ties are not too tight )    i.e. ( P = 0.7 )

   P ( x ≥ 18 ) = 1 - P( x ≤  17 )

                     = 1 - BINOMDIST ( 17, 30, 0.7, 1 )

                     = 1 -  0.08447006

                    = 0.9155