Aptitude  Probability
Exercise : Probability  General Questions
 Probability  Formulas
 Probability  General Questions
1.
Tickets numbered 1 to 20 are mixed up and then a ticket is drawn at random. What is the probability that the ticket drawn has a number which is a multiple of 3 or 5?
Answer: Option
Explanation:
Here, S = {1, 2, 3, 4, ...., 19, 20}.
Let E = event of getting a multiple of 3 or 5 = {3, 6 , 9, 12, 15, 18, 5, 10, 20}.
P(E) =  n(E)  =  9  . 
n(S)  20 
2.
A bag contains 2 red, 3 green and 2 blue balls. Two balls are drawn at random. What is the probability that none of the balls drawn is blue?
Answer: Option
Explanation:
Total number of balls = (2 + 3 + 2) = 7.
Let S be the sample space.
Then, n(S)  = Number of ways of drawing 2 balls out of 7  
= ^{7}C_{2} `  


= 21. 
Let E = Event of drawing 2 balls, none of which is blue.
n(E)  = Number of ways of drawing 2 balls out of (2 + 3) balls.  
= ^{5}C_{2}  


= 10. 
P(E) =  n(E)  =  10  . 
n(S)  21 
3.
In a box, there are 8 red, 7 blue and 6 green balls. One ball is picked up randomly. What is the probability that it is neither red nor green?
Answer: Option
Explanation:
Total number of balls = (8 + 7 + 6) = 21.
Let E  = event that the ball drawn is neither red nor green 
= event that the ball drawn is blue. 
n(E) = 7.
P(E) =  n(E)  =  7  =  1  . 
n(S)  21  3 
4.
What is the probability of getting a sum 9 from two throws of a dice?
Answer: Option
Explanation:
In two throws of a dice, n(S) = (6 x 6) = 36.
Let E = event of getting a sum ={(3, 6), (4, 5), (5, 4), (6, 3)}.
P(E) =  n(E)  =  4  =  1  . 
n(S)  36  9 
5.
Three unbiased coins are tossed. What is the probability of getting at most two heads?
Answer: Option
Explanation:
Here S = {TTT, TTH, THT, HTT, THH, HTH, HHT, HHH}
Let E = event of getting at most two heads.
Then E = {TTT, TTH, THT, HTT, THH, HTH, HHT}.
P(E) =  n(E)  =  7  . 
n(S)  8 
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