Probability of getting 2 balls of black colour from a box containing 3 red and 4 black balls is ?

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16 Apr 2010 Red and Black Ball

Probability of getting 2 balls of black colour from a box containing 3 red and 4 black balls is ?

OPtion

1) 5/9
2) 3/7
3) 1/4
4) 1/3
5) 5/7
6) 3/4
7) 2/7
8) 1/7
9) 3/5
10) 4/9

Solution

No. of methods of selecting 2 black balls out of 4 black balls is 4*3/2*1 = 12/2 = 6

No. of methods of selecting 2 balls out of total 7 balls is 7*6/2*1 = 21

Hence probability = 6/21 = 2/7

Correct Option: 7 Best Solution (11)

Dr.Dipin Singh   14 years AGO

Probability of getting 2 balls of black colour from a box containing 3 red and 4 black balls is (4/7)*(3/6) =2/7

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MP    14 years AGO

4/7 * 3/6 = 2/7 ..option 7

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Dolly   14 years AGO

Probability of getting 1st ball of black colour from a box containing 3 red and 4 black balls is 4/7 and
Probability of getting 2nd ball of black colour from a box containing 3 red and 3 black balls is 3/6.
so Probability of getting 2 balls of black colour from a box containing 3 red and 4 black balls is (4/7)*(3/6)= 2/7

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Saranjit Singh   14 years AGO

(4/7)* (3/6) = 2/7

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neena   14 years AGO

Probability = Total number of favorable cases / total number of cases
=2/7

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SUDESHNA SEN   14 years AGO

Total number of balls in the box =3 red + 4 black
= 7
Number of balls drawn = 2
Drawing 2 balls from the box

Total No. of Possible Choices = Number of ways in which the two balls can be drawn from the total 7
⇒ n = 7C2
= (7)!/(2)!*(5)!
=6*7/2= 21
The number of ways in which 2 balls of black colour can be drawn from the total 4= 4C2
=(4)!/(2)!*(2)!
=3*4/2= 6
Probability of getting 2 black balls
=6/21=2/7.............Option 7)

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ASHOK ROY   14 years AGO

Total number of balls in the box =3 red + 4 black
= 7
Number of balls drawn = 2
Drawing 2 balls from the box

Total No. of Possible Choices = Number of ways in which the two balls can be drawn from the total 7
⇒ n = 7C2
= (7)!/(2)!*(5)!
=6*7/2= 21
The number of ways in which 2 balls of black colour can be drawn from the total 4= 4C2
=(4)!/(2)!*(2)!
=3*4/2= 6
Probability of getting 2 black balls
=6/21=2/7.............Option 7)

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Karthik Pandiyan   14 years AGO

sample space =(4+3)=7
prob of getting 2 black color balls =2/7

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Ankur Pandey   14 years AGO

prob. of selecting 2 black balls=4C2/7C2=2/7

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susmit   14 years AGO

4c2/7c2

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shailender   14 years AGO

4*3/7*6=2/7

Like? Yes (1) | No