If the coefficient of rth and (r + 1)th terms in the expansion of (3 + 7x)29 are equal, then r equals
15
21
14
None of these
If in the expansion of (1 + x)m (1 - x)n, the coefficient of x and x2 are 3 and - 6 respectively, then m is
6
9
12
24
The number of subsets of {1, 2, 3, ..., 9} containing atleast one odd number is
324
396
496
512
C.
496
The total number of subsets of given set is 29 = 512
Even numbers are {2, 4, 6, 8}.
Case I : When selecting only one even number.
= = 4
Case II : When selecting only two even numbers
= = 6
Case III : When selecting only three even numbers
= = 4
Case IV : When selecting only four even numbers
= = 1
Therefore, number of ways
= 512 - (4 + 6 + 4 + 1) - 1
= 496
[ Here, we substract 1 for due to the null set]
A binary sequence is an array of 0's and 1's. The number of n-digit binary sequences which contain even number of 0's is
2n - 1
2n - 1
2n - 1 - 1
2n