Sum of Digits from 1 to 99

Add first and last digits. 1 + 99 = 100. 2 + 98 = 100. 3 + 97 = 100. Huh. There's a pattern here. 49 + 51 = 100 50 stands alone. 49 X 100 = 4900. Add 50. 49 X 100 + 50 = 4950. Ta Da!!!