sankasya ga nibai ni hueta.

It is read:

参加者が二倍に増えた。
さんかしゃ が にばい に ふえた。
Sankasha ga nibai ni fueta.

• 参加者（さんかしゃ） = participants
• 二倍（にばい） = double / twice as much
• 増えた（ふえた） = increased

参加者 means participant or participants.

It is made of:

• 参加 = participation
• 者 = person

So literally, it means people who participate.

In this sentence, it is naturally translated as participants.

が marks the thing that changed or the thing being described.

Here, the sentence is about what increased:

• 参加者が増えた = the participants increased / the number of participants increased

A helpful way to think about it is that 増える describes something increasing on its own, and が marks that thing.

In this sentence, に marks the resulting state.

So:

• 二倍に増えた = increased to double
• literally: became double through increasing

This is similar to other patterns where に marks what something becomes:

• 静かになった = became quiet
• 三人になった = became three people
• 二倍になった = became double

So 二倍に増えた means the amount ended up at twice the previous level.

This is a very common question.

• 増える = to increase, to grow, to go up
  
  • intransitive
• 増やす = to increase something, to make something increase
  
  • transitive

Here, the sentence says the number of participants increased, without naming a person who caused it:

• 参加者が二倍に増えた。 = The participants doubled. / The number of participants increased to twice as many.

If you used 増やした, you would need someone doing the increasing:

• 主催者が参加者を二倍に増やした。 = The आयोजers increased the number of participants to double.

Yes, 参加者が二倍になった is also natural.

The difference is slight:

• 二倍になった = became double
• 二倍に増えた = increased to double

So:

• なった focuses more on the final state
• 増えた focuses more on the process of increase

In many everyday situations, both are fine.

二倍に増えた means it became twice as much — in other words, it doubled.

This is one reason 二倍に is useful: it clearly shows the final amount is 2x the original.

A related phrase, 二倍増えた, can be confusing in Japanese, because some people interpret it differently. To avoid ambiguity, 二倍に増えた is a clear and common way to say doubled.

Japanese often leaves that implied.

English usually says:

• The number of participants doubled

But Japanese can simply say:

• 参加者が二倍に増えた

Even though 参加者 literally means participants, the intended meaning is really the number of participants.

This kind of omission is very common in Japanese when the meaning is obvious from the verb.

Yes, sometimes.

• 参加者が二倍に増えた。
• 参加者は二倍に増えた。

Both are possible, but the nuance is different:

• が presents participants as the thing that increased
• は makes participants the topic, as in as for the participants, they doubled

So が is a very natural neutral choice if you are simply reporting what happened.

Not completely. Japanese word order is more flexible than English, as long as the particles stay attached to the right words.

The standard order here is:

• 参加者が二倍に増えた

But you may also hear:

• 参加者が増えた
• 二倍に参加者が増えた is unusual in normal conversation and sounds marked

So while Japanese is flexible, the given order is the most natural and easiest for learners to use.

増えた is the past tense of 増える.

• 増える = increase / increases / will increase
• 増えた = increased

In Japanese, the past tense can also describe a completed change in state, so here it means the increase has already happened.

Yes. Depending on context, that is a very natural English translation.

Japanese often describes the change:

• 参加者が二倍に増えた = the participants increased to double

But natural English may describe the result:

• There were twice as many participants
• The number of participants doubled

Both capture the idea well.

二倍 is broadly used for things that can be measured or counted.

For example:

• 値段が二倍になった。 = The price doubled.
• 売上が二倍に増えた。 = Sales doubled.
• 人口が二倍になった。 = The population doubled.

So in this sentence, using 二倍 with participants is completely natural because participants can be counted.