Question

tính nhanh

10 + 20 + 40 + 60 + 80 + 90 + 100 

Answer 1

10 + 20 + 40 + 60 + 80 + 90 + 100 = 400

Answer 2

Ta ghép :

= ( 10 + 90 ) + (20 + 80 ) + ( 40 + 60 ) + 100
=     100        +     100       +     100        + 100

=                         400

Answer 3

=(90+10)+(80+20)+(60+40)+100

=100+100+100+100=400

Answer 4

\(10+20+40+60+80+90+100\)

\(=\left(10+90\right)+\left(20+80\right)+\left(40+60\right)+100\)

\(=100+100+100+100\)

\(=100.4\)

\(=400\)