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
In the expansion of , the coefficient of xr is
None of the above
C.
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