One - the trailing zeros are not significant.
One. The zeros are placeholders.
400000
Assuming you are dealing with whole numbers only: Half of the numbers round up and half round down. Half of ten thousand is five thousand. Therefore 400000 ± 5000 round to 400000 to the nearest 10000; except that numbers exactly half way round up, so the maximum is one less than this. → smallest to round [up] to 400000 is 400000 - 5000 = 395000 → largest to round [down] to 400000 is 400000 + 5000 - 1 = 404999
231.57 has five significant figures/numbers. All the numbers in 231.57 are significant.
100 centimetres = 1 metre so 400000 cm = 400000/100 = 4000 metres. Simple!
The figure 18.03 has a total of four significant numbers
400000 cubic meters = 105600000 gallons US
Three. All nonzero numbers are significant, and any zeros in between significant numbers are significant.
Because 10.00400 is 10.004, this has five significant digits (numbers).
about 400000
50
There are 5 significant figures.