Question

Please answer this question ☝️⬆️​

Answer 1

Answer:

5/81[10^(n+1)- 9n -10]

Step-by-step explanation:

let

y=5 + 55 + 555 +5555 +......n

y = 5{1+11+111+1111+....+n]

y = 5/9[9+99+999+....+n]

y = 5/9[(10 - 1)+(10^2 - 1) + (10^3 -1)+.....+(10^n - 1)]

y= 5/9[10+10^2+10^3+....+10^n] - (1+1+1+1+....+1]n

using formula

Sn = a(r^n - 1)/(r - 1)

where

a = 10

r = 10

y= 5/9[10*(10^n -1)/(10 -1) - n]

y= 5/9[10/9(10^n -1) - n]

y= 5/9[10^(n+1) - 10 - 9n]

Hope it may helps you :-)