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.
99.9 rounded to 2 significant figures is 1.0e2
A number with only 1 significant figure can't be rounded to 3 significant figures
6,256 rounded to 1 significant figure is 6,000
4000 has between 1 and 4 significant figures: if it is a rounded number, then it could have been 3999.9, for example, which would be rounded to 4000 to 1, 2, 3 or 4 significant figures.
It already is rounded to three significant figures.
5.000e-1 = 1.8394 When rounded to two significant figures, the answer would be 1.8
e A number that has only 1 significant figure can't be rounded to 3 significant figures
76.51 rounded to 1 significant figures would be 77
what is 0.0695712 to 1 significant figure
10000
Rounded to three significant figures, 1 nanometre is equal to 0.0000000394 inches.