a fair coin is tossed 10,000 times. Find a number m such that the chance of the number of heads being between 5000-m and 5000+m is approximately 2/3.
Also the number of heads is approximatly normally distributed .
Now a symetrical interval that contains of a normal distribution is (you get this from looking up a tail probability of backwards so to speak in a table of the standard normal distribution).
Now finish this yourself.