Question

Tính bằng cách thuận tiện nhất:

11 + 22 + 33 + 44 + 55 + 66 + 77 + 88 +99

Answer 1

( 11 + 88 ) + ( 22 + 77 ) + ( 33 + 66 ) + ( 44 + 55 ) + 99 

= 99 + 99 + 99 + 99 + 99 

= 99 x 5 

= 495

Answer 2

( 11 + 99 ) + ( 22 + 88 ) + ( 33 + 77 ) + ( 44 + 66 ) + 55

= 100 + 100 + 100 + 100 + 55

= 450

Answer 3

11 + 22 + 33 + 44 + 55 + 66 + 77 + 88 + 99

= ( 11 + 99 ) + ( 22 + 88 ) + ( 33 + 77 ) + ( 44 + 66 ) + 55

= 110 + 110 + 110 + 110 + 55

= ( 110 x 4 ) + 55

= 440 + 55

= 495.

Answer 4

 

= (11 + 99) + (22 + 88) + (33 + 77) + (44 + 66) + 55

= 110 +  110 +110 + 110 + 55

= 495

Answer 5

495