A. 1

B. 2

C. 3

D. -2

C_{1}/1 – C_{2}/2 + C_{3}/3 – C_{4}/4 +………. +(-1)^{n-1 }C_{n}/n =

The coefficient of x^{5} in the expression of (1+x)^{21}+(1+x)^{22}+……+(1+x)^{30} is

The coefficient of x^{7} in (ax^{2}-1/bx)^{11} is equal to the coefficient of x^{-7} in (ax-1/bx^{2}) then ab=

The number of non zero terms in the expansion of (8+2)^{101} - (8-2)^{101} is

The coefficients of three consecutive terms in the expansion of (1+x)^{n} are in the ratio 1:7:42, then n=