Time yourself!

To start, time yourself to see how long it takes for you to calculate the answers. Post your time in the comments! And do not use a calculator!
(Note: #1 does not need to be written out in full.)

1. 2^100 - 2^99


2. 6! + 7!


3. 198/6


4. 678+789


5. 100^(-1/2)


6. 1234+2345+3456+...+6789


7. (2^15)(5^16)


8. 155^2 - 154^2