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RBI Assistant Prelims 2015 Sitting 1 Paper
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© examsnet.com
Question : 44
Total: 100
In a bag there are 7 red balls and 5 green balls. Three balls are picked at random. What is the probability that two balls are red and one is green in colour?
29
44
21
44
27
44
23
44
19
44
Validate
Solution:
Total number of balls in the bag = 7 + 5 = 12
Total possible outcomes Selection of 3 balls out of 12 balls
=
12
C
3
=
12
×
11
×
10
1
×
2
×
3
=
220
Total favourable outcomes = Selection of 2 balls out of 7 red balls and selection of 1 ball out of 5 green balls
=
7
C
2
×
5
C
1
=
7
×
6
1
×
2
×
5
=
105
Required probability
105
220
=
21
44
© examsnet.com
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