JEE Advanced2018MathematicsProbabilityActual
Paragraph: There are five students S 1 , S 2 , S 3 , S 4 and S 5 in a music class and for them there are five seats R 1 , R 2 , R 3 , R 4 and R 5 arranged in a row, where initially the seat R i is allotted to the student S i , i = 1,2 , 3,4 , 5 . But, on the examination day, the five students are randomly allotted the five seats Question : For i = 1 , 2 , 3 , 4 Let T i denote the event that the students S i and S i +
Options
- A1 15
- B1 10
- C7 60
- D1 5
Correct answer
C. 7 60
Step-by-step solution
n T 1 ∩ T 2 ∩ T 3 ∩ T 4   = T o t a l - n T 1 ¯ ∪ T 2 ¯ ∪ T 3 ¯ ∪ T 4 ¯ = 5 ! -   4 C 1 4 ! 2 ! -   3 C 1 . 3 ! 2 ! +   3 C 1 3 ! 2 ! 2 ! +   2 C 1 2 ! 2 ! +   4 C 1 . 2.2 ! - 2 =     14 Probability = 14 5 ! = 7 60