A bag contains 9 identical balls, of which are 4 are blue and 6 are green. Three balls are taken out randomly from the bag after one another. Find the probability that all three balls are blue?

(a) \frac {5}{8}

(b) \frac {6}{19}

(c) \frac {5}{21}

(d) \frac {4}{7}

The question was posed to me in examination.

I would like to ask this question from Multiplication Theorem on Probability in chapter Probability of Mathematics – Class 12

NCERT Solutions for Subject Clas 12 Math Select the correct answer from above options

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Right choice is (c)

5

21

For explanation I would say: Since 6 balls are green, the probability of first ball to be drawn is green =

6

9

The probability of the first ball to be green, 8 balls are left and 5 out of them are green =

5

8

If the first two balls are green, then the probability of the third ball to be green =

4

7

According to multiplication theorem,

6

9

.

5

8

.

4

7

=

5

21