There are 4 signifigant figures in 19.83
Three of them.
1 in 1 km. 1, 2 3 or 4 in 1000 m since it is ambiguous.
1.0*103
1.0 x 10^3
5 of them.
There are 4 signifigant figures in 19.83
Six.
4
0.990
Three of them.
1 significant figure.
1000 and another 1000 1000 1000
Rounded to three significant figures, 1000 square feet is equal to 0.0230 acres.
There are 5 sig. figs. Rule: Zeros to the right of a decimal point and to the right of a number are significant. 12.380 cm [5] 169.00 m [5] 3.010 mL [4]
(4.73*1000*0.568)+1.61 = 2688.25 meaning that it has 6 significant figures
Just calling it a "1000-sided shape" is fine. It is too much trouble to search for fancy name for figures with many sides.