# Example 14 - Chapter 16 Class 11 Probability

Last updated at May 29, 2018 by Teachoo

Last updated at May 29, 2018 by Teachoo

Transcript

Example 14 On her vacations Veena visits four cities (A, B, C and D) in a random order. What is the probability that she visits A before B? 4 cities can be visited in any of following order S = ABCD, ABDC, ACBD, ACDB, ADBC, ADCB, BACD, BADC, BDAC, BDCA, BCAD, BCDA, CABD, CADB, CBDA, CBAD, CDAB, CDBA, DABC, DACB, DBCA, DBAC, DCAB, DCBA n(S) = 24 Let E be the event that she visits A before B Hence , E = ABCD, ABDC, ADBC, ACDB, ADBC, ADCB, CABD, CADB, CDAB, DABC, DACB, DCAB, Hence , E = ABCD, ABDC, ADBC, ACDB, ADBC, ADCB, CABD, CADB, CDAB, DABC, DACB, DCAB, n(E) = 12 P(E) = ( ) ( ) = 12 24 = Example 14 What is the probability that she visits (ii) A before B and B before C? S = ABCD, ABDC, ACBD, ACDB, ADBC, ADCB, BACD, BADC, BDAC, BDCA, BCAD, BCDA, CABD, CADB, CBDA, CBAD, CDAB, CDBA, DABC, DACB, DBCA, DBAC, DCAB, DCBA Let F be the event she visits A before B and B before C F = ABCD, ABDC, ADBC , DABC So, n(F) = 4 P(F) = ( ) ( ) = 4 24 = Example 14 What is the probability that she visits (iii) A first and B last? S = ABCD, ABDC, ACBD, ACDB, ADBC, ADCB, BACD, BADC, BDAC, BDCA, BCAD, BCDA, CABD, CADB, CBDA, CBAD, CDAB, CDBA, DABC, DACB, DBCA, DBAC, DCAB, DCBA Let G be the event she visits A first and B last G = ACDB, ADCB So, n(G) = 2 P(G) = ( ) ( ) = 2 24 = Example 14 What is the probability that she visits (iv) A either first or second? S = ABCD, ABDC, ACBD, ACDB, ADBC, ADCB, BACD, BADC, BDAC, BDCA, BCAD, BCDA, CABD, CADB, CBDA, CBAD, CDAB, CDBA, DABC, DACB, DBCA, DBAC, DCAB, DCBA Let H be the event she visits A either first or second H = ABCD, ABDC, ADBC, ACDB, ADBC, ADCB, BACD, BADC,CABD, CADB,DABC, DACB, So, n(H) = 12 P(H) = ( ) ( ) = 12 24 = Example 14 What is the probability that she visits (v) A just before B? S = ABCD, ABDC, ACBD, ACDB, ADBC, ADCB, BACD, BADC, BDAC, BDCA, BCAD, BCDA, CABD, CADB, CBDA, CBAD, CDAB, CDBA, DABC, DACB, DBCA, DBAC, DCAB, DCBA Let I be the event she visits A just before B I = ABCD, ABDC,CABD,CDAB,DABC,DCAB, So, n(I) = 6 P(I) = ( ) ( ) = 6 24 =

About the Author

Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.