>>> .3 - .2 - .1
-2.7755575615628914e-17

##</code><code>##

$  perl -E 'say  .3 - .2 - .1;'
-2.77555756156289e-17

##</code><code>##

> say .3 - .2 - .1;
0
> printf "%.50f\n", .3 - .2 - .1;
0.00000000000000000000000000000000000000000000000000