Actually, it's a pretty good test I think. To work it out in your head (in decimal you cheater! :D ) you need to know a bit about dealing with powers of two.

Actually, it's a pretty good test I think. To work it out in your head (in decimal you cheater! :D ) you need to know a bit about dealing with powers of two. <Spoiler alert!> So for example, if you happen to know that 2^32 is roughly 4 billion, then you can figure out that 2^64 is 2^32 squared. 4 billion is 4x10^9 .. so 2^64 is roughly 16x10^18.