question:9 basketball players are trying out to be on a newly formed basketball team. Of these players, 5 will be chosen for the team. If 6 of the players are guards and 3 of the players are forwards, how many different teams of 3 guards and 2 forwards can be chosen?
Options:
(A) 23
(B) 30
(C) 42
(D) 60
(E) 126
answer:(D)
Stream of consciousness:Out of 6 gaurds we have to select 3 -> selection means we use C -> so 6C3
Out of 3 forwards we have to select 2 -> selection means we use C -> so 3C2
Total ways = 6C3 x 3C2 = 60

question:If 1/2 of the air in a tank is removed with each stroke of a vacuum pump, what fraction of the original amount of air has been removed after 2 strokes ?
Options:
(A) 3/4
(B) 7/8
(C) 1/4
(D) 1/8
(E) 1/16
answer:(A)
Stream of consciousness:Left After 1st stroke = 1/2
Left After 2nd stroke = 1/2 * 1/2 = 1/4
So removed = 1- 1/4 = 3/4

question:An archer is shooting arrows from various distances. She shoots at a target from 40 yards, 50 yards, and 60 yards. The probability that she hits within the bullseye from 40 yards is 4/5, the probability that she hits within the bullseye from 50 yards is 3/4, and the probability that she hits within the bullseye from 60 yards is 2/3. What is the probability that she hits the bullseye at least once in three shots, one from each distance listed.
Options:
(A) 39/40
(B) 49/50
(C) 59/60
(D) 9/10
(E) 14/15
answer:
(C)
Stream of consciousness:The probability that she hits the bullseye at least once = 1 - (the probability that she misses the bullseye every shot)
The probability that she misses every shot = (prob that she misses from 40 yards)*(prob that she misses from 50 yards)*(prob that she misses from 60 yards)
Prob that she misses from 40 yards = 1 - 4/5 = 1/5; Prob that she misses from 50 yards = 1 - 3/4 = 1/4; Prob that she misses from 60 yards = 1 - 2/3 = 1/3
Thus the probability that she misses all shots = (1/5)*(1/4)*(1/3) = 1/60
Thus the probability that she makes at least one shot = 1 - (1/60) = 59/60