Pronounce /t/ or /d/?

[Van Khanh]

American people pronounce /d/ instead of /t/ in “ty” for 30,40,70,80,90.

Why don’t they do it with 20, 50,60 and 13,14,15,16,17,18,19.

Ex: Instead of saying /thirteen/, /fifty/, why don’t A people say /thirdeen/, /fifdy/?

Is there the rule for that?

Thanks

[Mister Micawber]

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Not all Americans do, and not consistently. And many just drop the /t/ entirely for 20 (/tweni/).

Flap-t (/d/ instead of /t/) often happens between vowel sounds or after a vowel and before a liquid.

With preceding (or succeeding) consonants, the /t/ sound is normally realized.
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Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mr. Micawber

[Yankee]

Hi Khahn

Americans also pronounce the t as a d in 50 and 60! When Americans pronounce 20, you might not hear anything at all where the t should be ("twenny"). But one thing is for sure, Americans never use a d sound in 20. So 20 seems to be the only exception to your "rule" here.

The t in "-teen" is always pronounced as t.

Why? I don't really know. I'm not sure that anyone does. That is a pronunciation style that has simply developed in the US.

Amy

PS
It's not only in the numbers 30 - 90 where the t can sound more like a d. For example, you might hear the word hearty pronounced very much like hardy.
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Amy
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ESL teacher, translator, and a native speaker of American English

[Mister Micawber]

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[Yankee]

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Good point, MM! I agree.
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_________________
Amy
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ESL teacher, translator, and a native speaker of American English