Between my first assessments I met some exercices that I don't know how to do them because I did not understand well the rules or maybe I applied in a wrong manner.
For instance:
The following numbers are expressed correct to two significant figures. Representing each number by the letter $x$, express the range in which each must lie, using an inequality.
a) 210 b) 64 c) 3.0 d) 0.88.
I don't understand what means these numbers and how to interpret that they are correct to two significant figures. It can be that 64 is an exact measured value rounded using two siginificant figures? So if $x=64$, then $$ 63.5\le x < 64.5. $$ Or 210 is an exact measure value rounded using two significant figures, so if $x=210$, then $$ 209.5\le x < 210.5. $$
Where can I find something about significant numbers and degree of accuracy? Thank you.
Your understanding seems correct to me.
Here are two links that may help you out. They discuss significant figures: https://www.chem.tamu.edu/class/fyp/mathrev/mr-sigfg.html.
https://courses.lumenlearning.com/physics/chapter/1-3-accuracy-precision-and-significant-figures/.
Good Luck!