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Joint Entrance Examination
Mathematics
Probability
Question 269
Question 269 of 417
Medium
MCQ
An urn has 9 balls: 3 red, 4 blue, 2 green. Three drawn at random without replacement. Find the probability all three have different colours.
A
2
/
7
2/7
2/7
B
1
/
21
1/21
1/21
C
2
/
23
2/23
2/23
D
1
/
3
1/3
1/3
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Official solution
\[P = \frac{{}^3C_1\times{}^4C_1\times{}^2C_1}{{}^9C_3} = \frac{24}{84}=\frac27\]
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