At least 1 and at most 7.
It could be 3,999,999.9 rounded to 7 significant figures;
It could be 3,999,999 rounded to 6 significant figures;
It could be 4,000,015 rounded to 5 significant figures;
It could be 4,000,429 rounded to 4 significant figures;
It could be 3,999,999 rounded to 3 significant figures;
It could be 4,049,999 rounded to 2 significant figures;
It could be 4,492,467 rounded to 1 significant figure.
One. The zeros are just placeholders.
3 significant digits because first zeros are just placeholders
Three. All nonzero digits are significant and zeros in between significant digits are always significant.
3
There are 4 significant figures in 6.741.
Three - all nonzero digits are significant.
4000000
Just the one and it is 4
One - the four. None of the trailing 0s are significant digits.
One - the zeros are placeholders unless indicated.
1 significant figure.
1 significant figure.
4
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 significant.