Tancet sample questions part 3

Probability questions
1. Out of 10 white, 9 black and 7 red balls, the number of ways in
which a selection of one or more balls can be made is
a. 881
b. 891
c. 879
d. 892
solution-
The white balls can be selected in 10 + 1 = 11 ways.
The black balls can be selected in 9 + 1 =10 ways.
The red balls can be selected in 7 + 1 = 8 ways.
Total number of ways = 11*10*8 = 880
But this includes the case when no ball is selected.
Hence the required number of ways = 880 - 1 = 879

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