Question

Bài 8:Tính tổng

a)100-99+98-97+...+4-3+2-1=

b)99-97+95-93+...+7-5+3-1=

Answer 1

99-97+95+93+...+4-3+2-1

=1+2+3+4+...93+95+97+99

=100+99+98+97+...97+98+97+100

=100+100+100+100+...100+100+100+100

=100*10

=100*10/2=500

Answer 2

a=50

b=50

Answer 3

100 - 99 + 98 - 97 + .......... + 4 - 3 + 2 - 1

= ( 100 - 99 ) + ( 98 - 97 ) + ....... + ( 4 - 3 ) + ( 2 - 1 )  ( 50 nhóm )

= 1 + 1 + ......... + 1 + 1 ( 50 số 1 )

= 1 . 50

= 50