question: Which one of the following is not a prime number?
Options:
(A) 2
(B) 3
(C) 5
(D) 9
(E) 7
answer: Stream of consciousness: 9 is divisible by 3. So, it is not a prime number. The answer is (D).


q: Ravi can do a piece of work in 30 days while Prakash can do it in 40 days. In how many days will they finish it together?
Options:
(A) 19 1/7 days
(B) 16 1/7 days
(C) 14 1/7 days
(D) 17 1/7 days
(E) 13 1/7 days
a: Stream of consciousness: 1/30 + 1/40 = 7/120
120/7 = 17 1/7 days The answer is (D).


question: The average of seven numbers is 18. The average of first three numbers is 14 and the average of last three numbers is 19. What is the middle number?
Options:
(A) 27
(B) 30
(C) 31
(D) 33
(E) 34
answer: Stream of consciousness: The total of seven numbers = 7X18 = 126
The total of first 3 and last 3 numbers is = 3 X 14+3 X 19 = 99
So, the middle number is (126 - 99 ) = 27 The answer is (A).


q: A car traveled from San Diego to San Francisco at an average speed of 51 miles per hour. If the journey back took twice as long, what was the average speed of the trip?
Options:
(A) 24.
(B) 34.
(C) 36.
(D) 42.
(E) 44.
a: Stream of consciousness: Let the time taken be = x
One way distance = 51x
Total distance traveled = 2 * 51x = 102x
Total time taken = x + 2x = 3x
Average speed = 102x/3x = 34 The answer is (B).


question: If 80 percent of the test takers taking an old paper and pencil GMAT exam answered the first question on a given math section correctly, and 75 percent of the test takers answered the second question correctly, and 5 percent of the test takers answered neither question correctly, what percent answered both correctly?
Options:
(A) 60 %
(B) 65 %
(C) 70%
(D) 75%
(E) 80%
answer: Stream of consciousness: {Total} = {First correctly} + {Second correctly} - {Both correctly} + {Neither correctly}
100 = 80 + 75 - {Both correctly} + 5
{Both correctly} = 60. The answer is (A).


question: A train running at the speed of 60 km/hr crosses a pole in 18 sec. What is the length of the train?
Options:
(A) 118
(B) 150
(C) 300
(D) 258
(E) 191
answer:

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
Stream of consciousness: Speed = 60 * 5/18 = 50/3 m/sec
Length of the train = speed * time = 50/3 * 18 = 300 m The answer is (C).