Native speakers will say like this: “Studying English paid off.”.
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: I got a job interview in a foreign country! Studying English finally paid off.
B: Congratulations! Good luck on it!
ネイティブスピーカーは次のように言います。
“Studying English paid off.”
(英語を勉強したかいがありました。)
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。
以下、会話例です。
A: I got a job interview in a foreign country! Studying English finally paid off. (外国で仕事の面接が決まりました！英語を勉強したことがついに報われました。)
B: Congratulations! Good luck on it! (おめでとう！頑張ってね！)
"Studying English really paid off!"
In this sentence you have analyzed your situacion and you have come to the conclusion that because you went ahead and studied English you now have a job you like. So you are stating how you feel about making this decision.
"I'm glad I made the decision of studying English."
This sentence is similar to the one up top. In this one you are being a bit more formal in stating that you are glad or satisfied in making the decision to study English. The end result of this decision is you getting a good job.
"Studying English really paid off!"（英語を勉強したかいがあった）
この文では、話し手が自らの状況を分析して、英語の勉強を始めたことで好きな仕事に就くことができたという結論に至っています。というわけで、この決断をしたことについての自らの気持ちを表してます。
"I'm glad I made the decision of studying English."（英語を勉強して良かったです）
これは上の文とよく似ています。ここでは、英語を勉強するという決断をして良かったと言って、よりフォーマルに表しています。この決断の結果として良い仕事に就けたわけです。
If you got or achieved somthing by doing something else then you use the term 'that paid off' meaning you wouldn;'t have got where you are without it
You could also say 'i'm glad' or 'good job' meaning your glad that you did it and it's improved you
I got the job! It was really worth studying English.
If studying English allowed you to get the job that you want, you can say that the work 'paid off'. This is a way of saying that your hard work enabled you to achieve success.
You could also say 'It was really worth studying English'. This means that the time you spent studying English was valuable, because you got the job you wanted. All the hard work 'paid off'!
I'm glad I took advantage of the opportunity to study English.
The two sentences you see provided above are great ways to express to your listener that you are glad that you studied English because you were able to get the job you wanted. In the second sentence you will see the term take advantage of something. This means to use a situation or circumstance to benefit oneself. This is a term that is commonly used in our everyday conversation.
上記二つの例文は「（やりたかった仕事に就けたので）英語を勉強して良かった」と伝える素晴らしい言い方です。
二つ目の例文には"take advantage of something"という表現が使われています。これは「〔状況を〕を活用する」という意味です。この表現は日常会話でよく使われます。
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