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a box contains 2 white balls , 3 black balls and 4 red balls . in how many ways can 3 balls be drawn from the box, if atleast one black ball is to be included in the draw.
Ans -3 out of 9 balls cane selected in 9C3 ways. then it is a case of arranging these 3 balls . the first ball can be arranged in 3 ways since we have 3 black balls , the second ball can be any of the remaing 8balls and third any of the remaining 7 balls . Where am i going wrong -please explain simple way
Answers (1)
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Look this can be solved in this manner . Total number of ways - None of the black balls is selected.
Now this is a case of selection and not arrangement.
Total number of ways = 9C3
None of the black balls is selected. It means we have to select 3 balls out of the other 6 balls . So number of ways = 6C3
Ans = 9C3 - 6C3