Sequence and SeriesMTP Mar 21Question 1844 of 128
All Questions

Find the sum to $n$ terms of the series: $7+77+777+\dots$ to $n$ terms:

Options

A$\frac{7}{9}n - \frac{7}{81}(10^{n+1} - 10)$
B$\frac{7}{9}(10^{n+1} - 10) + \frac{7n}{9}$
C$\frac{7}{81}(10^{n+1} - 10) - \frac{7n}{9}$
D$\frac{7}{9}(10^{n+1} - 10) + \frac{7n}{81}$
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Correct Answer

Option c$\frac{7}{81}(10^{n+1} - 10) - \frac{7n}{9}$

All Options:

  • A$\frac{7}{9}n - \frac{7}{81}(10^{n+1} - 10)$
  • B$\frac{7}{9}(10^{n+1} - 10) + \frac{7n}{9}$
  • C$\frac{7}{81}(10^{n+1} - 10) - \frac{7n}{9}$
  • D$\frac{7}{9}(10^{n+1} - 10) + \frac{7n}{81}$

About This Chapter: Sequence and Series

Paper

Paper 3: Quantitative Aptitude

Weightage

4-6 Marks

Key Topics

Arithmetic & Geometric Progressions

This chapter covers Arithmetic Progressions (AP) and Geometric Progressions (GP). Students learn how to find the nth term, sum of n terms, arithmetic/geometric means, and sum to infinity of a GP.

View Official ICAI Syllabus

Exam Strategy Tip

For complex 'sum of series' questions, a great hack is to substitute n = 1 and n = 2 into the question and the options to see which one matches, completely bypassing the formula.

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