Others have answered you already; I just want to add that in Perl 6 your code does what you expect. It achieves that by storing decimal numbers as fractions/rationals internally.

$ 
perl6
> say (42435.3408).perl
26522088/625
> say (42435.3408).WHAT
Rat()
> say 42435.3408 / 411.9936
103
> printf "%.20f\n", 42435.3408 / 411.9936
103.00000000000000000000
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