There is no set amount of classes you need to take.
The amount "sum of something" is limitless means, Its endless in number to the amount of classes you can take.
"There is no set amount "means that there is no set number or quantity of classes that is required for you to take.
"limitless"は、受けられる授業の数に制限がないことを表します。
"There is no set amount"は、受けなければならない授業の数に決まりがないことを表します。
If you want to indicate to someone that the amount of something that you need to take has no limit, you can use any of these :-
1. Limitless
Example: The amount of classes that I can take this year is limitless.
2. There is no limit
Example: There is no limit to the amount of classes I can take this year.
3. There is no minimum or maximum requirement
Example: There is no minumum or maximum requirement to the amount of classes I can take this year.
物事について制限がないことを表したいなら、以下の語句が使えます。
1. Limitless（無限の）
例：The amount of classes that I can take this year is limitless.（今年受けられる授業に制限はありません）
2. There is no limit（制限はない）
例：There is no limit to the amount of classes I can take this year.（今年受けられる授業に制限はありません）
3. There is no minimum or maximum requirement（上限・下限はない）
例：There is no minumum or maximum requirement to the amount of classes I can take this year.（今年受けられる授業に制限はありません）
Native speakers will say like this: “There's no limit".
There are lots of other ways to say it, but this one is the most accurate and most commonly used.
Here is an example on how to use this in a conversation:
A: How many classes must I take for this subject?
B: There is no limit, take as many or as few as you want.
ネイティブスピーカーなら次のように言うでしょう：
“There's no limit"（制限はない）
他にもいろいろな言い方ができますが、これが最も正確で一般的です。
会話で使うと次のようになります：
A: How many classes must I take for this subject?
［訳］この教科は何クラスとらないといけないんですか？
B: There is no limit, take as many or as few as you want.
［訳］制限はありません。好きなだけとってください。
There are many expressions to describe something with no limit. If there is an abundance of something such as a buffet. "Unlimited" is a great word to use. You can also say there's no limit if the situation has no maximum amount.
制限がないことを表す表現はたくさんあります。例えばビュッフェのようにたくさんのものがあるときには、"Unlimited"が使えます。もし上限がないということなら、"there's no limit"（制限がない）と言うこともできます。
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