Rationale: 6a2 = 6 * 2a * 2a = 24a2
The answer: (D)
Question: The edge of a cube is 2a cm. Find its surface?
Options:
(A) 24a8
(B) 24a4
(C) 24a1
(D) 24a2
(E) 24a7

Rationale: K + 2K +3 + 3K - 4 + 5K +1 = 11K
(11K -1)/4 = 63
11K = 63 * 4 = 252
K = 252 / 11 = 22 10/11
The answer: (A)
Question: If the average (arithmetic mean) of the four numbers K, 2K + 3, 3K 4 and 5K + 1 is 63, what is the value of K?
Options:
(A) 22 10/11
(B) 15 3/4
(C) 22
(D) 23
(E) 25 3/10

Rationale: It doesn't matter which type of card you choose, so:
Probability of choosing 1st card: 6/20
Probability of choosing 2nd card of the same type: 5/19
Probability of choosing 3rd card of the same type: 4/18
Multiply and you get 1/57
The answer: (C)
Question: A marble shop contains 6 blue marbles, 7 red marbles, and 7 green marbles. If 4 marbles are purchased at random from the shop, what is the probability that the 4 marbles will be blue?
Options:
(A) 5/19
(B) 9/20
(C) 1/57
(D) 15/57
(E) 15/684