Answer: (D)
Question: The H.C.F. of two numbers is 12 and their L.C.M. is 600. If one of the numbers is 480, then the other is:
Options:
(A) 11
(B) 10
(C) 8
(D) 15
(E) 12
[CoT]: [Other number = (12 x 600)/480 = 15.]

Answer: (C)
Question: 95 white and black tiles will be used to form a 10x10 square pattern. If there must be at least one black tile in every row and at least one white tile in every column, what is the maximum difference between the number of black and white tiles that can be used?
Options:
(A) 75
(B) 80
(C) 85
(D) 90
(E) 95
[CoT]: [Answer = C
Please refer diagram below
95 - 10 = 85]

Answer: (C)
Question: A train 640 m in length crosses a telegraph post in 16 seconds. The speed of the train is?
Options:
(A) 22 kmph
(B) 77 kmph
(C) 144 kmph
(D) 71 kmph
(E) 88 kmph
[CoT]: [S = 640/16 * 18/5 = 144 kmph]

Answer: (D)
Question:

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
Three people took GMAT practice tests in which the minimum and maximum possible scores are 200 and 800, respectively. They each took a test 3 times, and no one scored below 510 or over 780. If the individual ranges of the three people's scores in those 3 practice tests were 20, 90 and 130, what is the difference between the maximum and minimum possible ranges of all their scores put together.
Options:
(A) 70
(B) 80
(C) 90
(D) 140
(E) 170
[CoT]: [According to the information in the question the maximum range would be between 510 and 780(270). The minimum range would be the greatest range for any one individual, which is listed in the problem as 130. So the difference between these would be 270-130 or 140.]