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I'm watching a drama and there's a scene with a closeup of a cheque. It shows
the box where you would write the amount to pay, which I've parsed as below.
What is `金` used for and how is it read? `金額` already specifies it's an amount
of money plus there are two different yen symbols used.

> 金額 ￥ 金壱億伍阡萬円也

=

> 金額・￥・金・壱億伍阡萬・円・也

=

> (amount)・(yen symbol)・ **(?)** ・(一億五千万)・(another yen symbol)・(exact amount /
> "only")
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2018-01-20T17:45:06.717
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2018-01-21T11:47:26.493
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question
kanji numbers
Filling out a cheque - 金
This type of 金 is a prefix that just indicates the following number is an
amount of money. It's read as きん. For example, 金三万円 (read きん さんまんえん) means
"30,000 yen (of money)". This is occasionally used in certain serious
financial contexts, particularly in places where
[大字](https://en.wikipedia.org/wiki/Japanese_numerals#Formal_numbers) are still
used.

Practically, the only chance for a layperson to write this type of 金 is when
they prepare money envelopes such as
[祝儀袋](https://en.wikipedia.org/wiki/Sh%C5%ABgi-bukuro). See [how to prepare
祝儀袋](https://wedding.rakuten.co.jp/guest/goshugi/writing/) (in Japanese). The
majority of Japanese people have never seen nor used checks in Japan.
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2018-01-20T20:55:33.267
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Writing "金" at the beginning of numbers such as monetary amounts is to prevent
altering or falsification. Possible altering is to add another number before
the digit string. Therefore, it is important not to leave a gap between "金"
and the beginning of the numbers so that not any numbers are added.

Further more, we use "壱, 弐, 参, 拾, 阡, 萬 and 圓" instead of "一, 二, 三, 十, 千, 万,
and 円" respectedly in order to prevent altering. They used "円" in the example
given by OP, but we usually use "圓" for "円".

I think you can easily understand that "一", "二" and "三" are easily altered
into "五".  
"十", "千" and "万" could be changed into "五", too.
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2018-01-21T10:55:33.663
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answer