Tính bằng cách nhanh nhất 10+12+14+16+18+20=? ; 378+219 - 78=? ; 164+179+236+321=? ;1+3+5+7+9+11+13+15+17+19 =?

Đáp án:

 90;519;900;100

Giải thích các bước giải:

 10+12+14+16+18+20

=10+10+2+10+4+10+6+10+8+20

=10x5+(2+8)+(4+6)+20

=50+10+10+20

=90

378+219-78

=(378-78)+219

=300+219

=519

164+179+236+321

=100+64+100+79+200+36+300+21

=100x2+200+300+(64+36)+(79+21)

=200+200+300+100+100

=900

1+3+5+7+9+11+13+15+17+19

=(1+19)+(3+17)+(5+15)+(7+13)+(9+11)

=20+20+20+20+20

=20x5

=100

Tính bằng cách nhanh nhất:

a)10+12+14+16+18+20

=(10+20)+(12+18)+(14+16)

=30+30+30

=90

b) 378+219 - 78

=(378-78)+219

=300+219

=519

c)164+179+236+321

=(164+236)+(179+321)

= 400+500

=900

d)1+3+5+7+9+11+13+15+17+19 

=(1+19)+(3+17)+(5+15)+(7+13)+(9+11)

=20+20+20+20+20

=100