Question

A) 21+42+63+84+...2100? b) 4+8+12+16+...480? c)25+50+75+100+...400? d)10+20+30+40+...+490? e)6+12+18+...1200? f)30+60+90+120+...+900? g)15+30+45+60+...600? suma gaos dau coroana cine stie

Answer 1

a)21+42+63+84+......+2100=
=100×(21+2100):2=
=100×2121:2=
=50×2121=106050

b)4+8+12+16+......+480=
=120×(4+480):2=
=120×484:2=
=120×242=29040

c)25+50+75+100+......+400=
=16×(25+400):2=
=16×425:2=
=8×425=3400

d)10+20+30+40+.......+490=
=49×(10+490):2=
=49×500:2=
=49×250=12250

e)6+12+18+......+1200=
=200×(6+1200):2=
=200×1206:2=
=100×1206=120600

f)30+60+90+120+......+900=
=30×(30+900):2=
=30×930:2=
=30×465=13950

g)15+30+45+60+.....+600=
=40×(15+600):2=
=40×615:2=
=20×615=12300