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

Rationale: Speed of the boat in still water = (80+100)/2 = 90 kmph. Speed of the stream = (100-80)/2 = 10 kmph
The answer: (A)
Question: The speed of a boat in upstream is 80 kmph and the speed of the boat downstream is 100 kmph. Find the speed of the boat in still water and the speed of the stream?
Options:
(A) 90, 10 kmph
(B) 35, 27 kmph
(C) 50, 60 kmph
(D) 45, 55 kmph
(E) 45, 65 kmph

Rationale: Total distance = 8 Km
Total time = 50 Km
Time taken to cover the distence of 3 Km = 50*2/5 = 20 min = 1/3 hours
Remaining distance = 8 - 3 = 5 Km
Required speed = 5/1/3 = 15 Kmph
The answer: (B)
Question: Avinash covers a distance of 8km in 50 minutes. If he covers 3km distance in 2/5th of time then, What speed should he maintain to cover the remaining distance in the remaining time?
Options:
(A) 10 Kmph
(B) 15 Kmph
(C) 25 Kmph
(D) 27 Kmph
(E) 30 Kmph