18 The total number of terms in the expansion of $(x+a)^{100}+(x-a)^{100}$ after simplification is

If the integers $r>1, n>2$ and coefficients of $(3 r)$ th and $(r+2)$ nd terms in the Binomial expansion of $(1+x)^{2 n}$ are equal, then

The two successive terms in the expansion of $(1+x)^{24}$ whose coefficients are in the ratio $1:4$ are

The coefficient of $x^n$ in the expansion of $(1+x)^{2 n}$ and $(1+x)^{2 n-1}$ are in the ratio

If the coefficients of 2 nd , 3 rd and the 4 th terms in the expansion of $(1+x)^n$ are in AP, then the value of $n$ is