nedan ga nibai ni natta.

値段 means price.

In this sentence, it refers to the price of something already understood from context. Japanese often leaves out details that English would state explicitly, so 値段が二倍になった can mean:

• The price doubled.
• The price became twice as much.

が marks 値段 as the thing that underwent the change.

So:

• 値段が = the price (as the subject of the change)
• 二倍になった = became double

A natural English translation does not always need a literal subject marker, but grammatically が shows that the price is what changed.

二倍 means two times, double, or twice as much.

Here it does not mean plus two times more added on top. It means the final amount became 2x the original amount.

For example:

• if something was 100 yen
• and it became 200 yen
• then you can say 値段が二倍になった

The に marks the resulting state of a change.

The pattern is:

• A が B に なる
• A becomes B

So in this sentence:

• 値段が = the price
• 二倍に = into double / to double
• なった = became

That is why 二倍に is used: it shows what the price changed into.

なった is the past tense of なる, which means to become.

So:

• なる = become
• なった = became

In this sentence, 値段が二倍になった literally means:

• The price became double.

More natural English:

• The price doubled.
• The price became twice as high.

Because this sentence describes a change.

• だった is the past form of だ and simply means was
• なった comes from なる and means became

Compare:

• 値段は二倍だった。
  = The price was double.
  This just describes a state.

• 値段が二倍になった。
  = The price became double. / The price doubled.
  This shows a change from one state to another.

Yes, 値段は二倍になった is also possible.

The difference is nuance:

• 値段が二倍になった
  focuses on the price as the thing that changed
• 値段は二倍になった
  presents the price as the topic, often with a contrastive feeling such as as for the price...

In many situations, both are natural. Learners should know that が is very common when introducing or highlighting what changed, while は is common when the price is already the topic of conversation.

Yes, in this sentence it is essentially the same.

• 値段が二倍になった = The price doubled

Japanese often expresses this idea with X倍になる:

• 三倍になった = became triple / tripled
• 五倍になった = became five times as much

So 二倍になった is a very standard way to say doubled.

Because Japanese often omits information that is clear from context.

If people are already talking about, for example, eggs, rent, or train tickets, then just saying 値段が二倍になった is enough.

English often prefers to make this explicit, but Japanese frequently leaves it out when it is obvious.

Yes. 倍 is very productive.

Examples:

• 一倍 = one time as much
• 二倍 = double
• 三倍 = triple / three times as much
• 四倍 = four times as much

So you can say:

• 売り上げが三倍になった。
  = Sales tripled.
• 人口が四倍になった。
  = The population became four times larger.

It is read ねだん.

The full sentence is read:

ねだん が にばい に なった。

Useful readings here:

• 値段 = ねだん
• 二倍 = にばい

Yes, but it means something slightly different.

• 値段が上がった = The price went up
• 値段が二倍になった = The price doubled

So 上がった tells you the price increased, but not by how much.
二倍になった tells you the exact scale of the change: it became twice the original price.

It is neutral and plain in style.

• 値段が二倍になった。 = plain form
• 値段が二倍になりました。 = polite form

So the sentence as written is fine in casual conversation, narration, or informal writing. If you are speaking politely, you would usually use なりました instead of なった.