[tex]\bold{1.} \ 9 \ dam=\boxed{90 \ m}; \\ \ \ \ \ \ 100 \ cm=\boxed{1 \ m}. \\ \bold{2.} \ 536-90+70-300+1000=446+70-300+1000= \\ =516-300+1000=216+1000=\boxed{1216}.[/tex]
[tex]\bold{3.} \ 300 \approx 500; \\ 10 \approx 1; \\ 400 \approx 500.[/tex]