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 two significant digits.
It has 3 significant digits.
3 significant digits.
Five. All nonzero digits are significant and zeros in between significant digits are 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.
Five. All nonzero digits are significant and zeros in between significant digits are always significant.
890
50.4 has 3 significant digits.