It is a lot faster. You want to take about 5 or 10 minutes putting anything down you may need to remember (that I am sure you were looking at 10 seconds before you entered the room) so you don't have to fumble around trying to remember or figure out
The test is hard enough. Put down all calculations, tables, definitions you can that will help trigger your answers. This will take much of the stress of the test away.
Now if I give you 11000000 to convert, you write it down below :
128 64 32 16 8 4 2 1
1 1 0 0 0 0 0 0
Now take all the '1's
So 11000000 in decimal is 192.
This is much more useful than the hex conversion, you'll need to calculate binary values more often.
Also, you'll be sitting outside revising and then they'll tell you to go into the test room and start when you're ready. You aren't allowed to take anything in, but I suggest you go in, and write down everything you just revised. Then sit for a couple of minutes going over what you've written down.. maybe even do a sample calculation or something. Then you can start the actual test (they may even give you a sample test, just for you to get used to things).