Elementary confusion

[Keith]

Hi,

I am working through O'Reilly's "Learning Python". I am up to page 33,
and already I have a problem. The text outlines a cli entry about math
operators, all really straight forward;

.>>>a=3
.>>>b=4
.>>>b/2+a
 5
.>>>b/(2.0+a)
 0.8

This is so straight forward that I wasn't going to type it in, but I
did anyway, and got instead of '0.8' something I cannot account for. I
got '0.80000000000000004'.

So after 32 pages, I am already flumoxed. What is going on

-- 
Keith.