a , b , c , d , e sitting in a row what is the probability that a & b sitting adjacent .
total number of arrangement is = 5 ! = 120 favorable event i . e a and b can be arranged in 2 ! and the remaining can be arranged in 4 ! since ab can be in any of the four positions . so 4 ! * 2 ! / 5 ! = 2 / 5 answer : b
divide(multiply(multiply(const_4, const_2), permutation(const_3, const_3)), permutation(const_5, const_5))