S = 9 + 99 + 999 + + 9999999999

207/ - 500 CAU HOI KIEN THUC TONG HOP PHAN 1
500 CAU HOI KIEN THUC TONG HOP PHAN 1

207/ Tính tổng : S = 9 + 99 + 999 + + 9999999999 ?

…

S = 10 – 1 + 100 – 1 + + 10000000000 – 1

…

S = 11111111100