Răspuns :
4.
a)
7m+15dm-123cm+4257mm=
=7000mm+1500mm+1230mm+4257mm=
=8500mm+1230mm+4257mm=
=9730mm+4257mm=13987mm
b)
200g+320cg-80dg+2530mg=
=20000cg+320cg-800cg+253cg=
=20320cg-800cg+253cg=
=19520cg+253cg=
=19773cg
c)
4h15min30s+2h25min=
=6h40min30s=
=6×3600s+40×60s+30s=
=21600s+2400s+30s=
=24030s