On her vacations Veena visits four cities A, B, C and D in a random order. What is the probability that she visits: a.      A before B?         b. A before B and B before C? c.  A first and B last?  d. A either first or second? e. A just before B?

Explanation

Veena visits four cities A, B, C and D in a random order.


∴ Total number of arrangements, Veena can visit four cities A, B, C and D in 4!=24 ways.


(i) Out of 24 arrangements Veen a can visit city A before B in the following arrangements.


{ABCD, ABDC, ACDB, ACBD, ADBC, ADCB, CABD, CADB, CDAB, DABC, DACB, DCAB.}


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