990 has three significant figures.
900 of them.
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.
2 significant figures.
4
900 of them.
It has 3 significant digits.
3 significant digits.
It has two significant digits.
Five. All nonzero digits are significant and zeros in between significant digits are significant.
890
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.
Three significant digits.