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Find the sum to n terms …

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Find the sum to n terms of the sequence 5+55+555... to n terms
  • 2 answers

Raunak Chauhan 4 years, 2 months ago

Answer : 5+ 55+555+......n term 5(1+11+111+........n term) Dividing and multliply by 9 5/9(9+99+999.....n term) 5/9{(10-1)+(100-1)+1000-1)... n term} 5/9{(10+10²+10³+... n term)-(1+1+1+...n term)} 5/9[{10(10*n-1)/10-1)}-n] 5/81{10(10*n-1)-n

Gaurav Seth 4 years, 2 months ago

Answer:

 

Sum = 5 + 55 + 555 + …. n terms.
= 5/9 [9 + 99 + 999 + …. n terms]
= 5/9 [(10 – 1) + (100 – 1) + (1000 – 1) + … n terms]
= 5/9 [10 + 100 + 1000 ….. – (1 + 1 + … 1)]
= 5/9 [10(10n – 1)/(10 – 1) + (1 + 1 + … n times)]
= 50/81(10n – 1) – 5n/9

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