S = 9 + 99 + 999 + … + 9999999999

1000 CAU HOI KIEN THUC TONG HOPDOC

207/ Tính tổng : S = 9 + 99 + 999 + … + 9999999999 ?S = 10 – 1 + 100 – 1 + … + 10000000000 – 1 S = 11111111100