Customers are calling to a company, and each customer is equally likely to be a man or a woman. Using the Brownian motion approximation, estimate the probability that during the first n = 100 calls, the difference between the numbers of men and women will not exceed a = 10. (Advice: When applying the invariance principle from Section 1.1.2, set ξ_k = ±1. Note also that the inequality max_k≤n S_k ≤ b may be rewritten as max_k≤n(S_k/√n) ≤ b/√n , and it is reasonable to set b = a√n.)