Q: Which of the following is equal to (y+1)!/y!?
Options:
(A) y-1
(B) 1+(1/y)
(C) 1
(D) y+1
(E) y
A: OK... Stream of consciousness: (y + 1)! = (y + 1) * x!
(y + 1)!/y! = y + 1
The answer is (D).

Q: There are 10 students named alphabetically from A to J. What is the Probability that A and D do not sit together if all 10 sit around a circular table?
Options:
(A) 2/9
(B) 2/5
(C) 7/9
(D) 4/5
(E) 8/9
A: OK... Stream of consciousness: Number of students = 10
Number of ways 10 students can sit around a circular table = (10 - 1)! = 9!
Number of ways A and D sit together (consider A and D as one entity) = (9 - 1)! = 8! * 2
Number of ways A and D do not sit together = 9! - (8! * 2)
Probability = (9! - (8! * 2))/9! = 1 - 2/9 = 7/9
The answer is (C).

Q: 4000 was divided into two parts such a way that when first part was invested at 3% and the second at 5%, the whole annual interest from both the investments is Rs.144, how much was put at 3%?
Options:
(A) 2800
(B) 2500
(C) 3000
(D) 3500
(E) 4000
A: OK... Stream of consciousness: (x*3*1)/100 + [(4000 - x)*5*1]/100 = 144
3x/100 + 200 5x/100 = 144
2x/100 = 56 e x = 2800
The answer is (A).

Q: From among the 36 students in a class, one leader and one class representative are to be appointed. In how many ways can this be done?
Options:
(A) 1360
(B) 1260
(C) 1060
(D) 1160
(E) 1460
A:
OK... Stream of consciousness: There are 36 students and every one has equal chance of being selected as a leader. Hence, the leader can be appointed in 36 ways. When one person is appointed as leader, we are left with 35 students. Out of these 35 teachers, we can select one class representative. So, a class representative can be selected in 35 ways. Hence, the number of ways in which a leader and class representative can be selected = 36 x 35 = 1260
The answer is (B).