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UPSC NDA Math Model Paper 8
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© examsnet.com
Question : 27
Total: 120
A bag contains 7 red and 4 blue balls. Two balls are drawn at random with replacement. The probability of getting the balls of different colors is:
28
121
56
121
1
2
None of these
Validate
Solution:
There are a total of 7 red + 4 blue = 11 balls.
Probability of drawing 1 red ball
=
7
C
1
11
C
1
=
7
11
.
Probability of drawing 1 blue ball
=
4
C
1
11
C
1
=
4
11
.
Probability of drawing
(
1
red
)
A
N
D
(
1
blue
)
ball
=
7
11
×
4
11
=
28
121
.
Similarly, Probability of drawing
(
1
blue
)
A
N
D
(
1
red
)
ball
=
4
11
×
7
11
=
28
121
.
Probability of getting the balls of different colors
=
28
121
+
28
121
=
56
121
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