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probability of getting 3 same colour balls is-

it is possible to get 3 black balls so-3C3 out of 9C3

3C3/9C3=1/84

It is possible to get 3 white balls so-4c3 out of 9c3

4C3/9C3=4/84

to add -1/84+4/84=5/84

Answer
As it is a selection,not required arrangement of balls Hence,we apply combination. Here total no. Of outcomes=9c3=84 (As no. Of balls are 9 & we have to take three balls at a time) P(getting 3 balls of same colour)=(3c3 + 4c3)/9c3. =5/84
Answer

ANS--C

Total number of balls=2+3+4=9

Number of ways of selecting 3 balls=9C3

Since we have to draw 3 balls and they should be of same colours. So we can take out black or white balls.

This can be done in 3C3 and 4C3 ways

probability=(3C3+4C3)/9C3=5/84

Answer

total no of balls are (2+3+4=9)  out of which we have to remove 3 balls which can be done in 9c3 ways. since we have to draw balls of same color so the balls can be either black or white  this can be done in 3c3 and 4c3 ways .

so probability is (3c3+4c3)/(9c3)=  5/84( permutation of selection)

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