Here, we have to find the sum of the series 5 + 55 + 555 + ..... upto n terms i.e 5 + 55 + 555 + ...... to n terms = 5 ⋅ [1 + 11 + 111 + ..... to n terms] =
5
9
.[9+99+999+....... to n terms ] =
5
9
.[(10−1)+(102−1)+(103−1)+......... to n terms ] =
5
9
.[(10+102+103+........ to n terms )−n] As we know that, Sn=a(