Area under the curve

Hi John, I have a little problem with this question. The results of an accountancy exam are normally distributed with a mean score of 58 and a standard deviation of 10. What is the percentage probability that a student will score more than 80 (to 2 decimal places)? --->Correct Answer The percentage probability that a student will score more than 80 is 1.39% Calculate the Z score: Z-score = (x - µ)/? Z = (80 - 58)/10 = 2.2 Look up this number on the standard normal distribution table: 0.4861 This gives us the area under the normal curve between the mean and 80. The area under the curve above 80 will therefore be 0.5 - 0.4861 = 0.0139, or 1.39% **I understand everything but the part of "the area under the curve above 80 will be 0.5" How should I calculate that to end with 0.5? Thank you.