I have questions about the difference between "until" and "to". Can I say "write down from one to seven"?. How about using "until"? "write down from one until seven"? Are both okay? Can someone give me a brief explanation what's the difference between those two.

And these two sentences too.

(a). The participants are students aged 15 to 20

(b). The participants are students aged 15 until 20.

My friend said that (b) is incorrect. What's the difference?

I'm confused since in my native language, I only have one word to use. Thanks in advance!

Parts of speech: to is a preposition and until can be preposition or a cojnunction.

'To' is commonly used to refer to movement as, She is going to the park.

'Until' refers to the limit with reference to time.

They lived with him until he was successful in business.

They walked up to (not until) the public square and returned.

As far as the sentence you have given, I think you can express it this way:

"The participants are students aged between 15 and 20."
Thanks. But how about the sentences i mentioned above? I am still confused. Emotion: sad
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The participants are students aged 15 to 20.

The participants are students aged 15 until 20.

With regard to these sentences neither 'to' nor until is correct.

You can say this: Count from one to hundred.

When used along with 'from' ' to' denotes the upper limit. When 'to' (preposition) occurs alone, it commonly refers to the place of destination.

I think the explanation on 'until' given in my previous post is clear.