Question

Find the sum of of the first n terms
of 5-55-55------​

Answer 1

Answer:

is it minus or is it only numbers

Step-by-step explanation:

if it's numbers then

S=5+55+555+.......n terms

S=5(1+11+111.... nterms)

now multiply and divide by 9

so, S=5(9+99+999+.... nterms)/9

now split 9 as 10-1

so,S= 5( 10+100+1000.....n terms)/9 -( 1+1+1+1+1+... n terms)/9

now, use GP

S=5(10(10^n -1 )/10-1) /9 - n/9

so, 50(10^n -1)/81 -n/9

or 50(10^n -1)-9n/81

So final Answer is 50(10^n -1)

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81