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Question:

The number of ways of choosing 10 objects out of 31 objects of which 10 are identical and the remaining 21 are distinct, is?

221

220

220−1

220+1

Solution:

Correct option is A.220Find the total number of waysGiven that there are 31 Objects in which 10 are identical and 21 are distinctThe number of ways of choosing 0 identical and 10 distinct=1× 21CThe number of ways of choosing 1 identical and 9 distinct=1× 21CThe number of ways of choosing 2 identical and 8 distinct=1× 21CThe number of ways of choosing 3 identical and 7 distinct=1× 21CThe number of ways of choosing 4 identical and 6 distinct=1× 21CThe number of ways of choosing 5 identical and 5 distinct=1× 21CThe number of ways of choosing 6 identical and 4 distinct=1× 21CThe number of ways of choosing 7 identical and 3 distinct=1× 21CThe number of ways of choosing 8 identical and 2 distinct=1× 21CThe number of ways of choosing 9 identical and 1 distinct=1× 21CThe number of ways of choosing 10 identical and 0 distinct=1× 21C[ nC0+ nC1+ nC2+. nCn=21C0+ 21C1+ 21C2 2121C11+ 21C12. 21[nCr=nCn−rTotal number of ways= 21C0+ 21C1+ 21C2... 21C10=2212Hence option (A) is correct