Binomial and Geometric · Superchallenge problem

In an election between A and B, $10{,}000$ undecided voters each choose A or B with probability $\dfrac12$, independently, and a bloc of $100$ further voters all vote for A. Using the normal approximation with a continuity correction on the number of undecided voters who choose A, estimate the probability that A gets more votes than B. Give your answer to four decimal places.