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For example, when JAXA launches a rocket, or people count the seconds to the
New Year, do they use し or よん to count 4? do they use しち or なな to count 7?
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2011-07-31T20:35:58.903
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2011-08-03T05:47:07.187
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question
usage numbers
How do you do a countdown?
Usually when you count, you use `よん` for '4' and `なな` for '7'. That applies to
when you [count down](https://www.youtube.com/watch?v=JDSkhsbHwXI).

> じゅう きゅう はち **なな** ろく ご **よん** さん に いち

However, in some situations, pronouncing a certain sequence of numbers became
so frequent end became a fixed expression. In that case, '4' and '7' may be
pronounced `し` and `しち`, respectively. That includes a situation of counting
up:

> いち に さん **し** ご ろく **しち** はち きゅう じゅう
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2011-07-31T21:14:36.757
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2015-05-13T06:35:27.857
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answer