Question

Tính nhanh:

99-97+95-93+.....+7-5+3-1

Answer 1

= (99 - 97)+.....+(3-1)

=2+2+2+....+2

=2.25 = 50 

Answer 2

ta có:99 - 97 + 95 - 93 + 91 - 89 + ... + 7 - 5 + 3 - 1 
= (99 - 97) + (95 - 93) + ... + (7 - 5) + (3 - 1) = 25x2=50