SOLUTION: According to a survey, college students make an average of 11 calls per day on their mobile phone. Moreover, 80% of the students surveyed indicated that their parents pay for their

Question 815721: According to a survey, college students make an average of 11 calls per day on their mobile phone. Moreover, 80% of the students surveyed indicated that their parents pay for their mobile phone expenses.
If 20 students are selected at random, what is the probability that:
(i) All 20 have their parents pay for their mobile phone expenses?
(ii) At least 8 have their parents pay for their mobile phone expenses?
(iii) No more than 5 students pay for their own mobile phone expenses?
p=0.8 q=0.2
(ii) P(x≥8)= 1- P(x<8)
= 1- 1 - P(0) - P(1)....P(8)???
= 1- 20C0(0.8)^0(O.2)^20.....20C7(O.8)^7(0.2)^13 ???
Can you help me to solve all this questions?im lost...thank you very much for your coorporation.

Answer by ewatrrr(24785) (Show Source): You can put this solution on YOUR website!

 

Hi,

80% of the students surveyed indicated that their parents pay for their mobile phone expenses. 20 students selected at random. 

Binomial Probability Distribution Values: 

Note: The probability of x successes in n trials is: 

P = nCx*  where p and q are the probabilities of success and failure respectively. 

In this case p = .8 & q = .2 and n = 20  nCx = 



(i) P(x=20) = (.8)^20(.2)^0 = .0115  0r 1.15%

(ii) At least 8 have their parents pay for their mobile phone expenses?

P(x≥8)= 1- P(x≤7)**  TI Calculator:  1 - binomcdf(20,.80,7)= .999998

excel function : 1 - BINOMDIST(7,20,0.8,TRUE)

(iii) No more than 5 students pay for their own mobile phone expenses? 

         TI Calculator:  binomcdf(20,.80,5) = .00000018

excel function : BINOMDIST(5,20,0.8,TRUE)

If You do not have access to a TI Calculator or an Excel Worksheet,

might recommend STATTREK.com as a reference. 

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