Let ε1,ε2,...,ε2n be independent random variables such that P(\varepsilon_i\equal{}1)\equal{}P(\varepsilon_i\equal{}\minus{}1)\equal{}\frac 12 for all i, and define S_k\equal{}\sum_{i\equal{}1}^k \varepsilon_i, \;1\leq k \leq 2n. Let N2n denote the number of integers k∈[2,2n] such that either Sk>0, or S_k\equal{}0 and S_{k\minus{}1}>0. Compute the variance of N2n. integrationprobability and stats