Giải thích các bước giải: \(B= 10 + 5 + 10² + 55 + 10³ + 555 + ...... + 10^{n}n + 55555555.....5555\)
\(B= 10 + 10² + 10³ +....+ 10^{n}n + 5. ( 1 + 11 + 111+ .....+ 1111111.....1111)\)
\(B= 10 + 10² + 10³ +....+ 10^{n}n +\frac{5}{9}95( 9 + 99+ 999+ .......+ 9999999.....9999)\)
\(B= 10 + 10² + 10³ +....+ 10^{n}n + \frac{5}{9}95(10-1 + 10²-1+10³-1+.......+ 10^{n}n -1)\)
\(B= 10 + 10² + 10³ +....+ 10^{n}n + \frac{5}{9}95(10+ 10²+10³+.......+ 10^{n}n-n)\)
\(B=( \frac{5}{9}95+1) .(10 + 10² + 10³ +....+ 10^{n}n) -\frac{5}{9}95.n\)
\(B= ( \frac{14}{9})(10 + 10² + 10³ +....+ 10^{n}n) -\frac{5}{9}95.n\)