Many different answers may be available, but after all, it is just the way language develops
No it's spelled forty.
The number 45 in English is spelled forty-five. It is never spelled fourty-five.
The number 46 is spelled "forty six", normally hyphenated as "forty-six".
You have spelled it out correctly.
348 is spelled as three hundred forty-eight.
Sometimes 40 is spelled as forty because it sounds proper. Depending on what you are trying to say, either or could look better with the sentence.
47 is spelled out, 'forty-seven'.
"Forty thousand" in numbers is "40,000"
In American English four meaning 4 and forty meaning 40.
because that is how it sounds
It is spelled forty-four.
The number 48 is spelled forty-eight (hyphenated used an adjective).