Ques: Find the average of the first 9 natural numbers?
Options:
(A) 8
(B) 5
(C) 10
(D) 11
(E) 12
Ans: (B)
CoT: Average of the first 'n' natural numbers = (n + 1)/2
We get (9 + 1)/2 = 5

Ques: A man rows his boat 80 km downstream and 45 km upstream, taking 2 1/2 hours each time. Find the speed of the stream?
Options:
(A) 1 kmph
(B) 6 kmph
(C) 5 kmph
(D) 8 kmph
(E) 7 kmph
Ans: (E)
CoT: Speed downstream = d/t = 80/(2 1/2) = 32 kmph
Speed upstream = d/t = 45/(2 1/2) = 18 kmph
The speed of the stream = (32 - 18)/2 = 7 kmph

Ques: People standing in a straight line are wearing alternating colored shirts. The pattern of shirts begins with red, followed by green, blue, and yellow. This pattern continues (red, green, blue, and yellow) until it ends with a red shirt. If there are more than 4 people in line, which of the following cannot be the number of people in the line?
Options:
(A) 17
(B) 37
(C) 49
(D) 61
(E) 72
Ans: (E)
CoT: The correct answer should not take the form: 4x + 1. Hence, it is

Ques: A train 210 m long, running with a speed of 63 km/hr will pass a tree in?
Options:
(A) 15 sec
(B) 16 sec
(C) 18 sec
(D) 12 sec
(E) 25 sec
Ans: (D)

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
CoT: Speed = 63 * 5/18 = 35/2 m/sec
Time taken = 210 * 2/35 = 12 sec