Aptitude - Probability - Discussion
Discussion Forum : Probability - General Questions (Q.No. 2)
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 | |||
| = 7C2 ` | ||||
|
||||
| = 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. | |||
| = 5C2 | ||||
|
||||
| = 10. |
| P(E) = |
n(E) | = | 10 | . |
| n(S) | 21 |
Discussion:
116 comments Page 12 of 12.
Christiano ronaldo said:
7 years ago
I didn't understand this. Please, anyone, help me to get it.
Magnus The Great said:
7 years ago
@ALL.
According to me,
2 red
3 green
2 blue
Total Balls =7 Balls.
Note: (Always solve as *without replacement* unless otherwise stated)
Pr(1st Red & 2nd red...RR) = 2/7 * 1/6 = 1/21,
Pr(1st Green & 2nd Green..RG)=3/7*2/6= 1/7,
Pr( 1st Blue & 2nd blue..BB) = 2/7 * 1/6 = 1/21,
Pr(1st Red & 2nd Green...RG) = 2/7 * 3/6 = 1/7,
Pr(1st Red & 2nd blue...RB) = 2/7 * 2/6 = 2/21,
Pr(1st Green & 2nd blue...GB) = 3/7 * 2/6 = 1/7,
Pr(1st green & 2nd red ...GR) = 3/7 * 2/6 = 1/7,
Pr(1st blue & 2nd red.... BR) = 2/7 * 1/6 = 1/21,
Pr(1st blue & 2nd green...BG) = 2/7 * 3/6 = 1/7.
THEN
Pr( None is Blue) = RR or GG or RG or GR.
1/21 + 1/7 + 1/7 + 1/7.
= 10/21.
According to me,
2 red
3 green
2 blue
Total Balls =7 Balls.
Note: (Always solve as *without replacement* unless otherwise stated)
Pr(1st Red & 2nd red...RR) = 2/7 * 1/6 = 1/21,
Pr(1st Green & 2nd Green..RG)=3/7*2/6= 1/7,
Pr( 1st Blue & 2nd blue..BB) = 2/7 * 1/6 = 1/21,
Pr(1st Red & 2nd Green...RG) = 2/7 * 3/6 = 1/7,
Pr(1st Red & 2nd blue...RB) = 2/7 * 2/6 = 2/21,
Pr(1st Green & 2nd blue...GB) = 3/7 * 2/6 = 1/7,
Pr(1st green & 2nd red ...GR) = 3/7 * 2/6 = 1/7,
Pr(1st blue & 2nd red.... BR) = 2/7 * 1/6 = 1/21,
Pr(1st blue & 2nd green...BG) = 2/7 * 3/6 = 1/7.
THEN
Pr( None is Blue) = RR or GG or RG or GR.
1/21 + 1/7 + 1/7 + 1/7.
= 10/21.
HEMALATHA said:
6 years ago
@Pranav.
The answer is 62.
The answer is 62.
Summi said:
6 years ago
How come 7*6/2*1? please clear me.
ABI said:
5 years ago
The answer should be 5/7 right!
Because Probability = No.of favourable outcomes/Total outcomes.
=5/7.
Since, if both balls r not blue then they have to be either red(2) or green (3).
Thus,2+3 is 5.
So, option D is correct.
Because Probability = No.of favourable outcomes/Total outcomes.
=5/7.
Since, if both balls r not blue then they have to be either red(2) or green (3).
Thus,2+3 is 5.
So, option D is correct.
Priya said:
5 months ago
(2c0 3c1 + 2c1 3c1 + 2c2 3c0)/7c2.
Which is equal to (3+6+1)/21. = 10/21.
Which is equal to (3+6+1)/21. = 10/21.
Post your comments here:
Quick links
Quantitative Aptitude
Verbal (English)
Reasoning
Programming
Interview
Placement Papers