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Aptitude - Probability - Discussion

Discussion Forum : Probability - General Questions (Q.No. 12)
Probability
12.
A bag contains 4 white, 5 red and 6 blue balls. Three balls are drawn at random from the bag. The probability that all of them are red, is:
1
22
3
22
2
91
2
77
Answer: Option
Explanation:

Let S be the sample space.

Then, n(S) = number of ways of drawing 3 balls out of 15
= 15C3
= (15 x 14 x 13)
(3 x 2 x 1)
= 455.

Let E = event of getting all the 3 red balls.

n(E) = 5C3 = 5C2 = (5 x 4) = 10.
(2 x 1)

P(E) = n(E) = 10 = 2 .
n(S) 455 91

Discussion:
33 comments Page 2 of 4.
Akanksha said:   6 years ago
A box contains 6000 cards numbered 1 to 6000. One card is drawn at random from the box. Find the probability that the number is neither divisible by 4 nor 6? Please give me a solution.
(1)
Shiva said:   7 years ago
Why not 3/5 for selecting 3 red balls from total 5 red balls?
(1)
Somya said:   8 years ago
While calculating the term for red balls, why did we not consider the blue balls?
Chetan said:   8 years ago
Good explanation, Thanks @Rohit.
Subash said:   6 years ago
Can any one explain clearly.
Pavanmahesh said:   5 years ago
All of them red balls means why it can be a 15c3?
Laxman said:   5 years ago
@USHA.


For example, there are 3 red balls and you have to select two balls out of it then possible ways are,
6 ways let me show;
R1,R2 R1,R3 R2,R1 R2,R3 R3,R1 R3,R1.

In these selections, we have R1, R2 and R2, R1 same like the way we consider only one so that we have 3 choices but don't consider you are selecting 3 out of 3 balls.
Adu said:   8 years ago
Thanks all.
Divya said:   1 decade ago
How come 5C3 become 5C2? please explain.
Pandu raju said:   9 years ago
Thank you for the explanation.
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