How many significant figures are in 1000.1?

Answer 1

There are 5 sig fig.

The significant figures are all the digits between the first and last non-zero digits inclusive.

However, as trailing zeros are not normally written after a decimal point, if there are any it can be said that they are significant as they have been written, eg 1.2040 could be said to have 5 sig fig, not 4, as the zero after the '4' would not normally be written.

Answer 2

1000.1 has five significant figures.