OK -- I'll bite, as my 'nazi' nazi reflex kicks in.
If the 'and' implied a decimal place, then 'Three thousand and forty-two' would be 3004.2 or maybe 3040.2, but most likely 3042.
"Fourty two" is not a valid way of expressing a decimal fraction, as the 'fourty' has an implied decimal place. Three thousand point four two is recognised worldwide.