How many significant digits are there in 4000000?

Answer 1

There is one significant figure (which I assume you are referring to).

However there are 7 digits involved, of which all are significant. Each digit is important and special in its own right. None should be singled out as being different, as that is Digitist.

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Leaving aside the political correctness of the anti-digitism, the number of significant digits depends on the context. In the above example, if it is known that the number is not 3,999,999 nor 4,000,001 then all seven digits are significant. If it is known that the number is 4,000 thousand (not 3,999 thousand or 4,001 thousand) then there are 4 sig digs.