Question

find the sum of series 7+77+777+...

Answer 1

8641975300(til ten times 7)

Answer 2

7+77+777.......
taking 7 common
7(1+11+111......)
Multiplying and dividing by 9
7/9(9+99+999...... n times)
7/9(10-1 + 100-1 + 1000-1 +.....n times)
7/9(10+100+1000+....n times -(1+1+1.....n times))
now u i assume that u are familiar with gp(geometric progression)
use the sum for gp and you will get the answer