Four of them.
They have three significant digits
Five. All nonzero digits are significant and zeros in between significant digits are significant.
Three significant digits.
There are five significant digits.
This number has seven significant digits.
They have three significant digits
The significant digits are: 3701; so there are four such digits in the measurement. These are the digits that convey the degree of precision included. Leading zeroes and trailing zeroes do not add such meaning.
4
Five. All nonzero digits are significant and zeros in between significant digits are significant.
It has two significant digits.
3 significant digits.
It has 3 significant digits.
4 significant digits.
Five. All nonzero digits are significant and zeros in between significant digits are always significant.
Five. All nonzero digits are significant and zeros in between significant digits are always significant.
Five. All nonzero digits are significant and zeros in between significant digits are always significant.
000203 has 3 significant digits.