# NCERT Class 11-Math's: Chapter –9 Sequence and Series Part 13

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**Question 18:**

The third term of G.P. is . The product of its first terms is

(A)

(B)

(C)

(D) None of these

**Answer: (C)**

**Question 19:**

If 9 times the 9th term of an A.P. is equal to times the 13^{th} term, then the term of the A.P. is

(A)

(B)

(C)

(D)

**Answer: (A)**

**Question 20:**

If *x*, 2*y*, 3*z* are in A.P., where the distinct numbers *x*, *y*, *z* are in G.P. then the

common ratio of the G.P. is

(A) 3

(B)

(C)

(D)

**Answer: (B)**

**Question 21:**

If in an A.P., and , where S*r* denotes the sum of *r* terms of the A.P., then equals

(A)

(B)

(C)

(D)

**Answer: (C)**

**Question 22:**

Let denote the sum of the first terms of an A.P. If then is equal to

(A)

(B)

(C)

(D)

**Answer: (B)**

**Question 23:**

The minimum value of , is

(A) 2

(B) 4

(C) 1

(D) 0

**Answer: (B)**

**Question 24:**

Let denote the sum of the cubes of the first natural numbers and denote the sum of the first natural numbers. Then equals

(A)

(B)

(C)

(D) None of these

**Answer: (A)**

**Question 25:**

If denotes the nth term of the series then is

(A)

(B)

(C)

(D)

**Answer: (D)**

**Question 26:**

The lengths of three unequal edges of a rectangular solid block are in G.P. The volume of the block is and the total surface area is . The length of the longest edge is

(A)

(B)

(C)

(D)

**Answer: (A)**