# Lecture - 6 Chapter 9 Sequences & Series

 NCERT EXERCISE 9.3

Question 11. Evaluate $$\sum_{k=1}^{11} (2+3^k)$$

Question 12. The sum of first three terms of a G.P. is $$\frac{39}{10}$$ and their product is 1. Find the common ratio and the terms.

Question 13. How many terms of G.P. $$3, 3^2, 3^3, …$$ are needed to give the sum 120?

Question 14. The sum of first three terms of a G.P. is 16 and the sum of the next three terms is 128. Determine the first term, the common ratio and the sum to n terms of the G.P.

Question 15. Given a G.P. with a = 729 and 7th term 64, determine $$S_7$$.

Question 16. Find a G.P. for which sum of the first two terms is – 4 and the fifth term is 4 times the third term.

Question 17. If the 4th, 10th and 16th terms of a G.P. are x, y and z, respectively. Prove that x, y, z are in G.P.

Question 18. Find the sum to n terms of the sequence, 8, 88, 888, 8888… .