Question

1+12+23+34+45+56+67+78+89

Answer 1

=405 đó bạn

bạn tk mik nha

Answer 2

1 + 12 + 23 + 34 + 45 + 56 + 67 + 78 + 89

= (1 + 89) + (12 + 78) + (23 + 67) + (34 + 56) + 45

= 90 + 90 + 90 + 90 + 45

= 90 x 4 + 45

= 360 + 45

= 405

Answer 3

là 405 đó bn

Answer 4

\(1+12+23+34+45+56+67+78+89\)

\(=\left(1+89\right)+\left(12+78\right)+\left(23+67\right)+\left(34+56\right)+45\)

\(=90+90+90+90+45\)

\(=90\times4+45\)

\(=360+45\)

\(=405\)

Answer 5

1 + 12 + 23 + 34 + 45 + 56 + 67 + 78 + 89 = ????????????????????????????????????????????????????????????????

Answer 6

405 nha