In: Statistics and Probability
suppose that a hotel has 100 rooms and the hotel is accepting overbooking anticipating some cancellations. The probability for cancellation is 0.07.
a) What is the probability that somoen who made a reservation will be turned away if this hotel has allowed for 110 resevations?
b. 105 reservation
c. why did the answer to part b go down
We do this as a binomial probability.
Binomial Probability = nCx * (p)x * (q)n-x, where n = number of trials and x is the number of successes.
Please note nCr = n! / [(n-r)!*r!]. Also some standard formulae are as below.
(i) nCr = nCn-r eg 5C2 = 5C3
(ii) nC1 = n eg 5C1 = 5
(iii) nC0 = 1 eg 5C0 = 1 and
(iv) nCn = 1 eg 5C5 = 1
p, the probability that a customer turns up = 0.93
q = 1 - p = 0.07, is the probability of a cancellation
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(a) n = 110
Since the hotel has 100 rooms, this means that a customer will be turned away, when he comes after all 100 rooms are occupied. So we need to find P(X > 100) = P(101) + P(102) + P(103) + P(104) + P(105) + P(106) + P(107) + P(108) + P(109) + P(110)
P(x = 101) = 110C101 * (0.93)101 * (0.07)9 = 0.1228824
P(x = 102) = 110C102 * (0.93)102 * (0.07)8 = 0.1440512
P(x = 103) = 110C103 * (0.93)103 * (0.07)7 = 0.1486465
P(x = 104) = 110C104 * (0.93)104 * (0.07)6 = 0.1329243
P(x = 105) = 110C105 * (0.93)105 * (0.07)5 = 0.1009139
P(x = 106) = 110C106 * (0.93)106 * (0.07)4 = 0.0632412
P(x = 107) = 110C107 * (0.93)107 * (0.07)3 = 0.0314095
P(x = 108) = 110C108 * (0.93)108 * (0.07)2 = 0.0115916
P(x = 109) = 110C109 * (0.93)109 * (0.07)1 = 0.0028257
P(x = 110) = 110C110 * (0.93)110 * (0.07)0 = 0.0003413
Therefore P(X > 100) = P(101) + P(102) + P(103) + P(104) + P(105) + P(106) + P(107) + P(108) + P(109) + P(110) = 0.7588276 0.7588
We can use the excel formula BINOMDIST(100,110,0.93,TRUE) which returns the value of P( X 100) which is 0.2412. Since we need P(X > 100), we do 1 - 0.2412 = 0.7588 as found above.
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(b) n = 105
We need to find P(X > 100) = P(101) + P(102) + P(103) + P(104) + P(105)
P(x = 101) = 105C101 * (0.93)101 * (0.07)4 = 0.0752695
P(x = 102) = 105C102 * (0.93)102 * (0.07)3 = 0.0392160
P(x = 103) = 105C103 * (0.93)103 * (0.07)2 = 0.0151751
P(x = 104) = 105C104 * (0.93)104 * (0.07)2 = 0.0038772
P(x = 105) = 105C105 * (0.93)105 * (0.07)0 = 0.0004906
Therefore P(X > 100) = P(101) + P(102) + P(103) + P(104) + P(105) = 0.1340284 0.134
use the excel formula BINOMDIST(100,105,0.93,TRUE) which returns the value of P( X 100) which is 0.866. Since we need P(X > 100), we do 1 - 0.866 = 0.134 as found above.
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(c) The answer in part (b) has gone down as the number of overbookings have reduced. Therefore the chances for not getting a room reduces and hence the probability value has come down.