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NDA Math Probability
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© examsnet.com
Question : 78
Total: 100
Two similar boxes Bi (i = 1, 2) contain (i + 1) red and (5 – i – 1) black balls.
One box is chosen at random and two balls are drawn randomly. What is the probability that both the balls are of different colours?
[NDA I 2015]
1/2
3/10
2/5
3/5
Validate
Solution:
Consider the two given boxes
Box I → Red (2) Black(3)
Box II → Red (3) Black(2)
Probability of different colored balls in box 1 is
2
×
3
5
C
2
=
6
10
=
3
5
Probability of different colored balls in box 2 is
3
×
2
5
C
2
=
6
10
=
3
5
So if one box is chosen at random, the probability of different colored ball is
1
2
×
3
5
+
1
2
×
3
5
=
3
5
© examsnet.com
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