All bout Digit

2^1 = 2, 2^2 = 4 2^3 = 8 2^4 = 16......,and the pattern of last digits follow like this.. 2,4,8,6,2,4,8,6.... So after every 4 powers the pattern repeats therefore we can now say that last digit of 2^100 is 6. Now, 2^4=16 2^9=256 2^12=4096 2^16=65536.....and the pattern of 2nd last digits with last digit as 6 follows as 1,5,9,3,7,1,5,9,3,7....... So now we can calculate that 2nd last digit of 2^100 will be 7.
Therefore 6+7=13.