a) {[(620+22):6-(850+25):35]×15}:30=
=[(642:6-875:35)×15]:30
=[(107-25)×15]:30
=(82×15):30
=1230:30
=41
b) {4450-[3600-(90-50)×25]}:50=
=[4450-(3600-40×25)]:50
=[4450-(3600-1000)]:50
=(4450-2600):50
=1850:50
=37
c) {[(520+180):2x5x10+5x11]:5-511}:100=
=[(700:2×5×10+55):5-511]:100
=[(350×5×10+55):5-511]:100
=[(17500+55):5-511]:100
=(17555:5-511):100
=(3511-511):100
=300:100
=3
