Aptitude - Probability - Discussion
Discussion Forum : Probability - General Questions (Q.No. 7)
7.
In a class, there are 15 boys and 10 girls. Three students are selected at random. The probability that 1 girl and 2 boys are selected, is:
Answer: Option
Explanation:
Let S be the sample space and E be the event of selecting 1 girl and 2 boys.
| Then, n(S) | = Number ways of selecting 3 students out of 25 | |||
| = 25C3 ` | ||||
|
||||
| = 2300. |
| n(E) | = (10C1 x 15C2) | ||||||
|
|||||||
| = 1050. |
 P(E) = |
n(E) | = | 1050 | = | 21 | . |
| n(S) | 2300 | 46 |
Discussion:
54 comments Page 5 of 6.
Shikha said:
8 years ago
I am not able to understand this answer please some one clear my doubt.
Sanu said:
8 years ago
We don't have to use nCr here it should be nPr.
We are only selecting the girls and not arranging, so no need of using combination here.
We are only selecting the girls and not arranging, so no need of using combination here.
Deel khus said:
8 years ago
@Prabhu.
They are multiplied bc.
The rule of calculating probability is that if getting a or b then we must be added the probability and if getting a and b then its probability must be multiplied.
They are multiplied bc.
The rule of calculating probability is that if getting a or b then we must be added the probability and if getting a and b then its probability must be multiplied.
Shekhar Gupta said:
8 years ago
To select boy and girls are mutually independent events. So they are multiplied.
Bhargavi said:
7 years ago
On which table 1050/2300 can be divisible?
(2)
Mahendra said:
7 years ago
But without applying the formula, trying to solve it, gives me a different answer.
The probability of selecting girl = 10/25.
Next, Probability of selecting 1 boy = 15/24 (24 because 1 girl is already selected).
Next, the Probability of selecting another boy = 14/23 (23 because 1 boy and 1 girl were already selected) (14 because 1 boy was already selected before).
So,
P(E) = n(E)/n(s) = (10x15x14)/(25x24x23)=2100/13800=21/138 = 7/46.
The probability of selecting girl = 10/25.
Next, Probability of selecting 1 boy = 15/24 (24 because 1 girl is already selected).
Next, the Probability of selecting another boy = 14/23 (23 because 1 boy and 1 girl were already selected) (14 because 1 boy was already selected before).
So,
P(E) = n(E)/n(s) = (10x15x14)/(25x24x23)=2100/13800=21/138 = 7/46.
(3)
Jeevan said:
7 years ago
@Mahendra.
See, we can select 1girl and 3 boys in 3 ways{gbb, bgb, bbg} and you have followed only one way which is {gbb}. It is not a correct way.
Here, we have to Find the probability for 3 ways then sum those results, you will get 21/46 or As for every way it gives the result as 7/46 you can multiply it with 3 then you will get 21/46.
See, we can select 1girl and 3 boys in 3 ways{gbb, bgb, bbg} and you have followed only one way which is {gbb}. It is not a correct way.
Here, we have to Find the probability for 3 ways then sum those results, you will get 21/46 or As for every way it gives the result as 7/46 you can multiply it with 3 then you will get 21/46.
(2)
K Pradeep Kumar Reddy said:
6 years ago
What is the mistake in my approach?
Probability of selecting a girl = 10/25.
Probability of selecting a boy = 15/25.
Probability of selecting one girl and two boys is 10/25 + 2* 15/25 = 40/25 = 8/5.
Totally there are three combinations of selecting 1 Girl and 2 Boys.
GBB
BGB
BBG
So the total probability of selecting one girl and two boys is 3*8/5 = 24/5.
Probability of selecting a girl = 10/25.
Probability of selecting a boy = 15/25.
Probability of selecting one girl and two boys is 10/25 + 2* 15/25 = 40/25 = 8/5.
Totally there are three combinations of selecting 1 Girl and 2 Boys.
GBB
BGB
BBG
So the total probability of selecting one girl and two boys is 3*8/5 = 24/5.
(7)
Thanos said:
5 years ago
@Jay Lee Lord.
Thank You for your answer.
Thank You for your answer.
Karthick M said:
3 years ago
@Prabhu and @Priyaa.
The question is given as 1 girl and 2 boys. Given 'AND' we use simple of multiplication.
Suppose they are given In the question if 1 girl or 2 girls. We use simple subtraction.
That's all.
The question is given as 1 girl and 2 boys. Given 'AND' we use simple of multiplication.
Suppose they are given In the question if 1 girl or 2 girls. We use simple subtraction.
That's all.
(8)
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