One. Although integers ending in 0 are ambiguous. If the number is known to be accurate to the nearest ten, for example, then there are 3 significant digits.
Three of them.
One of them.
111.0
Because March 14th or 3-14 are the first 3 digits of pi which are 3.14
There are 4 signifigant figures in 19.83
Three of them.
4.
One of them.
111.0
80.00 has 4 significant figures.
How many
Because March 14th or 3-14 are the first 3 digits of pi which are 3.14
5 of them.
Six.
8000 feet = 8000 feet.
There are 4 signifigant figures in 19.83
4 significant figures.